A top Nigerian basketballer, Michael Ojo died at the age of 27 during a training session in the Serbian capital on Friday.
The Lagos-born Ojo previously played for Red Star Belgrade.
Red Star’s spokesperson Igor Vujicin said: “We are deeply saddened by the news.
His former team released a statement mourning his loss describing him as a “cheerful giant”.
The club couldn’t confirm the cause of death, but local media reported that Ojo suffered a heart attack.
The 2.16 metre (7ft 1in) centre played for Florida State University in the United States before coming to Europe to start his professional career.
After a brief stay with the Belgrade team FMP Zeleznik, he journeyed to European giants Red Star, where he spent two seasons, quickly becoming a fan favourite.
Ojo had been without a club since June 30 but was still training with Red Star.
Red Star said: “The sudden and shocking death of Michael Ojo has deeply affected everyone — players, coaches and the management of a club that accepted him from the first day, and that he considered his own”.
EuroLeague also extended condolences to Ojo’s family, teammates, coaches, “and many fans who enjoyed his performances”.