Dallas Mavericks say Kristaps Porzingis has been involved in an altercation at a nightclub in his native Latvia.
After video showed the forward with a bloody forehead, the Mavericks said on Sunday: "It is our understanding that Kristaps was jumped and assaulted outside of a club."
However, they did not provide further details.
Video of the aftermath of the incident obtained by TMZ showed an agitated Porzingis in a torn shirt, pushing someone out of the way and approaching a group of men, before several people stopped him and urged him to calm down.
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The 23-year-old was acquired by Dallas in a blockbuster deal with the New York Knicks before the trading deadline but has not played for the team.
He missed the 2018-19 season after tearing a ligament in his left knee, in what turned out to be his final game for the Knicks in February 2018.
Porzingis will be a restricted free agent on July 1, and the Mavericks have said they intend to sign him to a long-term contract.