The N.B.A. is investigating whether Nets guard Kyrie Irving violated the league’s coronavirus protocols after a video emerged Monday on social media that appeared to show him at a crowded indoor party without wearing a mask.

The N.B.A.’s health protocols prohibit players from attending indoor social gatherings of 15 or more people. If the league determines that Irving broke these rules, he could be fined 1/81.6 of his estimated $33 million annual salary (more than $400,000) for each game he has to miss while quarantining. The length of the quarantine depends on several factors, such as the setting of the violation and how long the player was there.

Sean Marks, the Nets general manager, said in a statement that the team was aware of the video, which it described as showing Irving at a “family gathering.”

“We are reviewing the circumstances with both Kyrie and the N.B.A. in order to determine compliance with health and safety protocols,” Marks said.

Representatives for Irving could not immediately be reached for comment.

It’s unclear when and where the gathering took place, but the video of it compounds puzzling aspects of the season for Irving, who has not played since Jan. 5 for what the team has called “personal reasons.”

Ahead of last Thursday’s game against Philadelphia, Nets Coach Steve Nash said that he had not heard from Irving and did not know why he wasn’t playing. Before Tuesday night’s game against Denver, Nash declined to say more than that the organization had been in touch with Irving.

“There’s been communication, but I think that’s all in-house,” Nash said. “We keep that to ourselves, and we try to figure out our home front privately.”

Asked if he was confident that Irving would return this season, Nash said: “Sure. Like I said, right now, I’ve got to focus on coaching this team and getting the best out of them. So I can’t make any predictions, prognostications about things that are outside of this building.”

In his statement, Marks said that Irving’s return had “yet to be finalized.”

“In the meantime, we will continue to stay focused on our organizational goals,” Marks said. “Kyrie will have the opportunity to address his absence when he is ready to do so.”

After Tuesday’s win over the Nuggets, the Nets were 6-6 for the season but 4-3 when Irving had played. He was off to a stellar start, averaging 27.1 points and 6.1 assists on 50.4 percent shooting in seven games. The Nets also went without Irving’s co-star, Kevin Durant, for a week because of the N.B.A.’s health protocols.

James Harden, the Houston Rockets guard, was fined $50,000 earlier in the season after attending an indoor party with more than 15 people on Dec. 21, the eve of the season’s opening night. Irving was also fined $25,000 that month, for refusing to speak to the media.