Manager Terry Collins downplayed the seriousness of the injury, calling it something Marcum experiences "every spring, pretty much."
Collins added that he expects the right-hander to make his final Grapefruit League start next week.
"He just wanted to get it cleaned up and get it done early so he could take a couple of extra days now," Collins said, "and he can go into his last start in the spring and extend himself a little bit."
Jeremy Hefner will start on Thursday in Marcum's place.
Marcum came to the Mets with a history of arm trouble, including a bout of shoulder stiffness last spring and an episode of elbow tightness that cost him two months last summer. He made his Grapefruit League debut on Feb. 23, then skipped a turn in the rotation to concentrate on his long-toss program. He last pitched on March 16, giving up two runs in four innings.
If Marcum misses any significant time, the Mets could face some serious rotation issues. Hefner is already filling in for Johan Santana, who is a lock to miss Opening Day. Jenrry Mejia is battling tendinitis in his forearm, leaving left-hander Aaron Laffey as the obvious choice to replace Marcum.
Even before learning of Marcum's injury, the Mets planned to begin stretching Laffey out as a starter; he will now make his rotation debut on Sunday.
In addition to Marcum and Santana, other Mets questionable for Opening Day include third baseman David Wright, second baseman Daniel Murphy and closer Frank Francisco.
Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDicomo. This story was not subject to the approval of Major League Baseball or its clubs.