The Nets announced on Tuesday that James Harden suffered a setback in his rehab from a hamstring injury that has kept him out in eight of Brooklyn's last nine games.
The setback occurred while Harden was on the court on Monday, and he underwent an MRI later that day.
Head coach Steve Nash said Harden "felt something in the ballpark of a strain," and they are "back to square one" in terms of his rehabilitation.
Harden will be out indefinitely, the team said, and updates "will be provided as appropriate," according to a team statement.
Prior to playing just four minutes on April 5 against the Knicks before reaggravating the injury, Harden was averaging 26.1 points, 11.2 assists, and 8.9 rebounds per game since joining the Nets.