On Tuesday, Dec. 21, Charlie Brown Jr. was walking through the lobby of the Mandalay Bay Resort and Casino in Las Vegas when he saw his friend Zylan Cheatham looking joyous.

Brown could tell just by looking at him that he had good news to share.

Earlier that day, Cheatham had found out that the Miami Heat wanted to sign him to a 10-day contract. He started screaming, jumping and running around his hotel room, where he had been staying to compete in a showcase of the best teams in the N.B.A.’s developmental league, the G League. Cheatham canceled plans to go home to Phoenix for Christmas, and when he called his mother to tell her, she jumped around, too.

Soon after, Brown heard another friend had gotten a call-up from the G League. And then one of Brown’s teammates on the G League’s Delaware Blue Coats did too.

“It was slowly happening around me,” Brown said.

A few hours later it happened to him. Brown’s agent called him as he was warming up for a game at the G League Showcase. The Dallas Mavericks wanted to sign him.

Brown and Cheatham are two of more than 80 players who have signed 10-day contracts with N.B.A. teams this season. Their opportunity has come because N.B.A. players, like everyone else, are facing the latest wave of the coronavirus. The virus, especially the Omicron variant, has depleted several N.B.A. rosters in recent weeks. A recent decision to shorten required isolation time for some infected players could help teams get their usual stars back sooner.

The league and players’ union have agreed to grant hardship exceptions to allow teams to temporarily sign players to fill in, even if they wouldn’t otherwise have the roster or salary cap space. Hardship exceptions and short-term deals existed before the pandemic, but until at least Jan. 19, teams can sign players to 10-day contracts to replace anyone who tests positive for the coronavirus as soon as they need them. The league is also requiring its 30 teams to sign replacement players if they have more than one player out with a coronavirus infection.

With dozens of players testing positive every week, these reinforcements help the N.B.A. avoid postponing more games — it has already done so nine times — when teams don’t have enough healthy players.

For some basketball pros, that has meant getting a call they’ve been waiting for their whole lives, an opportunity to be seen or a second chance they never saw coming.

“A dream come true to say the least,” Cheatham said. “It’s every hooper’s dream. It’s what you work for, especially competing in the G League for multiple years. This is kind of your Super Bowl or N.B.A. finals.”

The players signing 10-day contracts this month have included younger players like the 26-year-old Cheatham, who is just a few years out of college; older players who have spent years in the G League hoping for a chance; and N.B.A. veterans who had been out of the league and hoping for a comeback — players like Lance Stephenson, Isaiah Thomas and the 40-year-old Joe Johnson.

This time around, Johnson’s teenage son gets to be part of the fun.

“He asked me about a month ago, ‘Dad, when you was playing, what was I doing?’” Johnson told reporters. “I said, ‘You was in the back playing in the playroom.’”

On Monday, with all their regular starters out, the Minnesota Timberwolves used the hardship exception to sign Greg Monroe, a 31-year-old former lottery draft pick who last played in the N.B.A. in 2019.

Monroe woke up at 4 a.m. Monday to fly to Minneapolis from Washington, D.C. His first flight got canceled, and he finally got in around 11 a.m. to be tested for the coronavirus so he could play.

Hours later, Monroe played 25 minutes against the Boston Celtics, scoring 11 points to go with 9 rebounds and 6 assists in the Timberwolves’ win.

“I’ve been around the world and back, literally,” Monroe, who played in Germany and Russia in the last two years, told reporters. “But it felt great to be out there. Just a joy to be out there.”

A 10-day contract has typically been like a tryout for players, with several signees getting longer deals to stay with their teams for the rest of the season and beyond. The former players Kurt Rambis, Raja Bell and Bruce Bowen all turned these short deals into notable careers.

One recent example is Gary Payton II, who played on 10-day contracts for several teams before signing one with Golden State last year. This year, Payton has been critical to Golden State’s resurgence. At 29 years old, he seems finally to have found an N.B.A. home.

On Christmas, Golden State needed 14 minutes from Quinndary Weatherspoon, whom they signed on Thursday from their G League affiliate, the Santa Cruz Warriors. Weatherspoon, 25, came highly recommended by Klay Thompson, who had been guarded by Weatherspoon during scrimmages as he rehabbed his injuries with Santa Cruz. Weatherspoon came home from the G League Showcase and hours later left again to join Golden State.

“It’s been crazy,” Payton said. “Guys been waiting for this moment.”

Weatherspoon benefited from playing on the developmental team affiliated with the team that signed him. That makes a lot more familiar — the personnel, the system, the facilities.

Cat Barber, who was called up to the Atlanta Hawks from their College Park Skyhawks G League team, was similarly familiar with his new surroundings. He’s spent five years in the N.B.A.’s developmental league, rapping on the side, and never considered giving up this dream.

“Just the love for basketball that I’ve got,” Barber said. “A lot of people were telling me I’m right there, I’m that close, and I just stuck with it.”

Barber played 2 minutes in the Hawks’ Christmas loss to the Knicks and 4 minutes in a loss to the Bulls on Monday.

“I accomplished something that not a lot of guys do,” Barber said. “I’m proud of myself.”

There’s a financial benefit that can mean a lot, too. The typical salary for a G League player is $37,000 a year. Most 10-day contracts are signed for a prorated portion of the league’s minimum salary, which means most players signing 10-day contracts are making double their yearly G League salary in just 10 days in the N.B.A.

“Growing up you hear people always say: ‘Oh, you got to play basketball for the love of the game. The money will come. You don’t worry about that,’” Cheatham said. “But at the same time, anybody who has real problems or real situations with family or taking care of people knows having money is definitely beneficial.”

Brown got to Dallas on Wednesday and was immediately bombarded with group chats (from his former and current team), the playbook and instructions for the next few days. He guessed that he had stayed up until 3 or 4 a.m., with a wake-up call before 8 a.m. Thursday.

On Christmas, the Mavericks had six players unavailable because of the virus. That was the first game Brown was able to play in for Dallas. At one point, four of the five Mavericks on the court were replacements. Brown said Brandon Knight, an N.B.A. veteran signed as a replacement point guard, helped things run smoothly.

“The best thing you can do is prepare for any given situation,” Brown said. “It can happen any day, any hour. Being on your toes kind of helps you in a way because you’re overly prepared for the moment.”

Brown had never played on Christmas, the day when the N.B.A. highlights its best teams and biggest stars. He used to watch Christmas games with his father, Charles Brown Sr., back home in Philadelphia.

“My dad texted me earlier in the day. Nothing meant more to him than seeing me play on Christmas,” Brown said, “because I used to talk about it all the time.”

But the specter of the virus remains present for all of them.

Cheatham, who had appeared in just four N.B.A. games before his call-up, arrived in Miami on an off day for the Heat last week. They were set to play the Pistons next day, and he found himself introducing himself to his teammates on game day. He didn’t play in that game, but on Tuesday, he said he felt confident he could help if needed.

He also acknowledged the precarious nature of his position.

“To say you don’t worry about catching Covid would be blasphemy at this point,” Cheatham said. “Every time you open your phone you see a new case. And then you see guys are vaccinated and did all the things you did and still get Covid.”

He talked Tuesday about avoiding contact with others where possible, and making smart decisions despite the unpredictability of the virus.

On Wednesday morning, the Heat added Cheatham to their list of players out because of the league’s health and safety protocols.