|Besiktas just can't find consistency at the point guard position, with Carlos Arroyo's injury the latest news in an incident-packed season|
The Puerto Rico international suffered the injury during the Quarter-Final tie with Artland Dragons, which Besiktas won 2-0.
The club said in a statement: "An MRI scan taken has confirmed a tear in his left thigh.
"Arroyo, who has been instrumental in the Eagles' (Besiktas) recent surge, will be sidelined for up to six weeks."
The EuroChallenge Final Four tips off on 27 April.
Arroyo, 32, has averaged 10.1 points and 2.7 assists in the EuroChallenge.
He signed for the team at the end of December as a replacement for Deron Williams, who returned to the New Jersey Nets following the end of the NBA Lockout.
Besiktas swept Artland Dragons in their best-of-three Quarter-Final, with Arroyo playing in both games.
Besiktas won at Olin Edirne on Sunday, 76-64.
Winners of the Turkish Cup, Besiktas are fourth in the Turkish League (BEKO Basketbol Ligi) with 18 wins and five defeats.