Mets ace Jacob deGrom's bout with right forearm tightness has landed him on the 10-day injured list, manager Luis Rojas announced on Sunday.

Rojas labeled deGrom day to day on Saturday, and the right-hander had been shut down from throwing. But when the tightness didn't go away on Sunday morning, the team made the move, which is retroactive to Thursday.

"I'm frustrated," deGrom said. "I don't know what else to say. I mean, I guess it probably is good news whenever structurally everything looks good, but you go out there and try to throw a baseball and the forearm just doesn't feel good. The level of frustration right now is very high.

"You want to be out there trying to help your team win baseball games. I think that's where the frustration comes from. And then my job is to run out there every fifth day, and I haven't been able to do that. That's part of the frustration as well, but then you got to get over it and come up with the best plan to get healthy and hopefully stay out there."

deGrom underwent an MRI on Saturday that revealed no structural damage. Rojas said deGrom experienced similar tightness in a bullpen session before the All-Star break, and it flared up again during a side session the ace tried to throw during the break.

"This is something that we decided today," Rojas said. "He still has the tightness in his forearm, so until the tightness is resolved, he's not going to be able to throw. That's not going to be tomorrow, so that's why we're IL-ing him. Making sure that that's resolved and then he can throw, and then we can start probably having [him] play catch and go into a progression from what he does to have his start. That's why we're doing the move. He's still tight, still not able to throw, so he's feeling it."

The forearm tightness marks the latest in a series of injuries that have impeded deGrom throughout what has otherwise been a historically dominant start to the season. He missed two weeks with right side tightness in May, then exited his June 11 start with right flexor tendinitis, only to make his next start five days later, which he was forced to depart after three perfect innings with a sore right shoulder. He made his final four starts of the first half without further incident, though he opted to skip Tuesday's All-Star Game in light of those injury problems.

Despite all that, he finished the first half with a 1.08 ERA and a realistic chance to best Bob Gibson's 1968 1.12 ERA, the lowest qualified mark in the AL or the NL in the Live Ball Era.

"He's actually really good about it," Rojas said of deGrom dealing with the injury issues this season. "I had conversations with him before this one, where I tried to see where his state of mind is with these different injuries that he's had, and he's able to separate them. ... No different [with] this one today just talking to him in my office. His goal right now is to work on this and just get it over with and start pitching again. ... I think he's determined to just take care of this and progress into his next start."

Rojas said in his conversation with deGrom that it appears the previous injuries aren¡¯t related to the forearm tightness that has sidelined him to start the second half of the season.

"It's been different things from what [the doctors have said]," Rojas said. "We've had now two in the forearm, and they're both different. One was more in the flexor. This one is in a different spot. ... We've had the MRIs where they don't show structural damage and they don't show any correlation."