Reyes was examined by Mets team physician Dr. Struan Coleman on Thursday and underwent an MRI at New York's Hospital for Special Surgery, the release said.
The club will know more about the injury Friday, which is shaping up to be a critical day this season for the injury-plagued club.
The MRI revealed the tear.
Reyes felt pain behind his right knee while playing in an extended spring game Wednesday and was removed after three innings. The All-Star shortstop is currently on the disabled list with a calf strain.
Jesse Sanchez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.