The 29-year-old right-hander tore his right patellar tendon on March 15 while celebrating after getting the final out of Puerto Rico's win over the Dominican Republic at the World Baseball Classic. The projected timeline for a return was six to eight months.
"My goal was to be ready in six months," Diaz said Monday. "And I'm working on that."
Diaz said he was clocked in the low to mid-90s on Sunday, when he threw on an outdoor bullpen mound to a catcher in the crouching position for the first time since getting hurt.
"I know my stuff is there," Diaz said. "A main thing for me is how my knee is good and healthy. I feel healthy right now, and I'm pitching again. I just want to get that positive note to go home and relax, work hard for next year."
Buck Showalter has been encouraged by Diaz's progress, but the Mets manager said it's too early to determine whether a September return is possible.
"We're waiting for the medical signoff, and then there will be a decision to be made," Showalter said. "But that's a good thing to think that he would be considered. It'd be really exciting for everybody. Whether or not we go down that road, we're not there yet."
Diaz had 64 saves and a 4.00 ERA for the Mets from 2019 to 2021 then registered 32 saves with a 1.31 ERA and 118 strikeouts in 62 innings last season. He agreed in November to a five-year, $102 million contract, a record deal for a closer.