Reyes has been on the disabled list since May with a hamstring tendon problem.
Mets manager Jerry Manuel said before New York's 7-4 loss at Washington on Wednesday that doctors were trying to make a determination as to whether Reyes needs surgery.
The Mets say Reyes felt discomfort in the hamstring while running during his rehabilitation work Tuesday at a training facility on Long Island.
An MRI showed the new tear.
Reyes batted .279 with two homers, 15 RBIs and 11 steals in 36 games this season.