MINNEAPOLIS -- Twins closer Glen Perkins threw off flat ground for a fourth time on Wednesday as part of the rehab process for his strained left shoulder, and he is scheduled to throw his first bullpen session on May 23.
Perkins, on the 15-day disabled list retroactive to April 11, made 25 throws from 90 feet before Wednesday's game against the Orioles. He said he'll continue to throw off flat ground, including a few rounds of long toss, before he gets to his first bullpen session, which he said will be the first real test.
"That will be the big day," Perkins said. "I won't know much until I test it. Long toss and all that stuff like rehab feels good. But the real test will be throwing off a mound."
Perkins, a three-time All-Star, added that he's noticed a difference in his shoulder the last week or so after taking a day off during the club's off-day on Thursday.
"It feels good," Perkins said. "It's not like I've tested anything or pushed anything. But the rehab and strength tests have gone really well so far. I took an off-day during the last homestand after going two and a half weeks straight, and from that point, it's progressed really well."
There's no exact timetable for Perkins' return, but he appears to be on track for early to mid June if all goes well. He's also expected to need a short rehab assignment before returning.
"I'll probably pitch a time or two in the Minor Leagues," Perkins said. "I don't think I'll have to pitch much down there, but we'll see."
Perkins added it's been tough to be out and watch the Twins struggle in his absence, as they entered Wednesday with the worst record in the American League at 8-24.
"It's not only the losing but just not being able to be out there," Perkins said. "I haven't faced that much the last five years to not be able to play and not be able to participate. Knowing I could help is tough, but I can't change anything that's happened. Sixty-five appearances a year for five years catches up to you. So hopefully the time I've taken off will make me stronger down the stretch."
Rhett Bollinger has covered the Twins for MLB.com since 2011. Read his blog, Bollinger Beat, follow him on Twitter @RhettBollinger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.