Lagares was diagnosed with an intercostal strain Monday after undergoing an MRI at the Hospital for Special Surgery in Manhattan. He had departed Sunday's game at Citizens Bank Park in the 10th inning complaining of pain in his right rib cage.
The Mets promoted outfielder Matt den Dekker from Triple-A Las Vegas, although in reality den Dekker never left.
After 14-inning games Friday and Saturday, the Mets had demoted den Dekker before Sunday's game to add an extra arm, Dana Eveland, from the minor leagues. Den Dekker was due to fly to Las Vegas on Sunday night, but was told to remain in Philly after Lagares' situation worsened.
Normally players need to spend 10 days in the minor leagues after being optioned, but an exemption is made for a return in a shorter time frame if a DL move coincides.
Lagares had been scratched from Saturday's game against the Phillies with rib-cage spasms. He ended up pinch hitting in extra innings that day, but was only permitted to bunt -- not swing away.
He convinced the staff he was healthy enough to return to the lineup Sunday, but was forced to depart in the 10th inning when the rib cage became noticeably painful.
"I swung in the cage and didn't feel anything," Lagares said Sunday about his pregame workout. "During the game, in my last at-bat, I felt it a little more and I said, 'I have to stop. That's not normal.'"
With his flashy outfield play as well as improved performance at the plate this season, the 25-year-old Lagares had emerged as a lineup regular. He is hitting .288 with two homers and 18 RBIs in 156 at-bats.
With Lagares and Eric Young Jr. (hamstring) now on the disabled list, Curtis Granderson figures to be a regular in the outfield, with Chris Young, Bobby Abreu, Eric Campbell and den Dekker also seeing action.