Beltran, who will be out for at least 12 weeks following the surgery, missed half of his team's games last season due to ongoing problems with his right knee. He went on the disabled list on June 22.
The nagging injury prompted Beltran to have the knee procedure, apparently without the knowledge of the Mets, the official Major League Baseball website (MLB.com) reported.
"I'm sitting down with a pen and pad trying to figure some things out," Mets manager Jerry Manuel told reporters.
Beltran, a five-times All Star, is expected to resume baseball activities in 12 weeks, and is coming off a year in which he led the team with a .325 batting average and had 10 home runs in his limited action.
(Writing by Jahmal Corner in Los Angeles; Editing by Peter Rutherford)