The Mets said Harvey received a platelet-rich plasma injection and will begin rehab until pain-free. He was placed on the disabled list Friday.
Harvey, 28, lamented his health following Wednesday's start against the Cubs in which he allowed three home runs in four innings.
"My arm was just not working at all,'' said Harvey, who had a rib removed last year during surgery for thoracic outlet syndrome. "I think the last time I threw 87 [mph] with a fastball was probably freshman year of high school.''
The former ace is 4-3 with a 5.25 ERA in 13 starts.
"He was complaining about a tired arm, a dead arm," general manager Sandy Alderson said.
The Mets also placed second baseman Neil Walker on the 10-day disabled list with a partial tear of his left hamstring suffered in Wednesday's game. He also received a PRP injection and will start rehab immediately, the team said.
Alderson estimated Walker, who is hitting .270 with 9 home runs and 13 RBIs, could need two to three weeks of rehabilitation, then more time to rejoin the Mets. T.J. Rivera started at second base in the series opener against the Nationals.
The Mets recalled infielder Gavin Cecchinifrom Triple-A Las Vegas on Thursday. On Friday the Mets placed center fielder Juan Lagares on the 10-day disabled list after he broke his left thumb trying to make a diving catch during Thursday night's 8-3 home loss to theNationalsandrecalled Brandon Nimmo and Matt Reynolds.
Also Thursday, Alderson said RHP Noah Syndergaard won't throw for at least another four weeks as he continues to recover from a torn right lat muscle.Syndergaard last pitched April 30, and at the time of the initial diagnosis, he was told not to throw for about six weeks.
Alderson also said doctors found "loose bodies" in the elbow of lefty Josh Smoker, who went on the disabled list this week with a strained shoulder.
The Associated Press contributed to this report.
Mets in trouble with more injuries
Tim Kurkjian breaks down how the Mets' latest injury concerns will affect the team.