OAKLAND -- The Yankees placed left-hander Nestor Cortes on the 15-day injured list with a left groin strain on Thursday, retroactive to Monday. The club added righty Greg Weissert, activated slugger Giancarlo Stanton from the injured list and transferred outfielder Harrison Bader to the 60-day IL in corresponding moves.

Cortes said he first felt discomfort in his left groin area on the second or third pitch of his most recent outing, a 4-2 Yankees win over the Blue Jays on Sunday. The 27-year-old said he initially didn't know how serious the injury was, so he wrapped the area in the third inning and pitched through the pain, completing six innings.

The soreness persisted the day after, so Cortes underwent an MRI exam, which showed a Grade 2 strain. 

"During the game, I didn't think it was that big of a deal," Cortes said. "Obviously, I wanted to compete and give my team the best chance possible, so I grinded through it. I didn't know how bad it was until the MRI. Even the next day, I thought it was OK, but the fact that I was limping -- we needed the MRI."

Yankees manager Aaron Boone said he was optimistic that Cortes could return in mid-September, as the lefty is already doing some flat-ground baseball activity. There is not yet a timetable for Cortes' return.

"Hopefully it's not something that costs him more than a couple starts, and hopefully something maybe that serves him well and gives his body a little break," Boone said before Thursday's series opener vs. the A's at the Coliseum. "He's up and moving already. I actually threw with him out here. He's doing agility drills. He's hitting the ground already in the rehab process, so hopefully it's not something that costs him too much time."

The loss of Cortes is another blow to the club's pitching depth. He has been one of the Yankees’ best arms this season, posting a 2.68 ERA with 133 strikeouts over 131 innings.

Clarke Schmidt will take Cortes' place in the rotation, getting the start on Sunday in the  series finale.

Schmidt, who has a 2.18 ERA in 33 innings spanning 17 appearances (one start) in 2022, has impressed the Yankees with his growth from previous seasons, and Boone said racking up more big league experience has only helped him progress in the Majors.

"He's fearless," Boone said. "He's a really confident kid with really good stuff, and you feel comfortable putting him in any situation and knowing that he's got the gumption to kind of handle that."