Marcum will have surgery on Monday to repair an artery blockage that was causing numbness in his right hand.
Marcum allowed six runs on a career-high 11 hits, gave up five earned runs Saturday night against the Milwaukee Brewers and is 1-10 with a 5.29 ERA in 14 starts this season. Marcum said he had been experiencing tingling and a loss of feeling in his hand in his last two starts.
Marcum's WAR (wins against replacement) has declined each of the last three seasons and will be a free agent at season's end.
“I am certainly concerned,” Mets manager Terry Collins said. “I don’t want this thing to keep flaring up. Maybe the rest is the best thing for him at this time, I’ll talk to Shaun today also about it, where he stands and where we stand on it all. Eventually we’ll come up with a plan for the next two weeks."