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8/9/2014 1:38 A.M. ET

Third-base coach Vavra undergoing hip surgery

OAKLAND -- Twins third-base coach Joe Vavra didn't go on the club's current road trip through Oakland and Houston, as he's set to undergo surgery to repair a torn labrum in his left hip.

Vavra was diagnosed with the injury during the All-Star break in mid-July and hasn't coached third since then. Since the injury he had been serving as a bench coach with Paul Molitor moving from the bench to first-base coach and Scott Ullger moving from first to third.

"He's going to definitely going to have a full hip replacement surgery," Twins manager Ron Gardenhire said. "By the time we get off this trip, he'll be getting his surgery. And then they said maybe a week or so. But after that, he can return to the bench. But I don't think he'll be at third this year."

Gardenhire added that Molitor has done just fine in his new role at first-base coach, as he's able to help the baserunners pick up on things he sees from the opposing pitcher. Molitor had 504 stolen bases in his Hall of Fame career.

"He's good over there," Gardenhire said. "He has all the information for them. He sees things, and we've said this along, but Moli sees things other people can't. He reads pitchers a little bit easier."

No. 8 prospect May coming up to debut for Twins

OAKLAND -- The wait is over.

Highly regarded prospect Trevor May will make his Major League debut for the Twins on Saturday against the A's. The right-hander will be recalled from Triple-A Rochester to make his first big league start. The Twins optioned first baseman Chris Colabello to Triple-A after Friday's 6-5 loss to make room for May on the roster.

"It's definitely exciting," May said. "To have this happen is a little bit surreal. But I had the flight here to get that out of the way. Now that I'm in the clubhouse it feels like another day at the field, but I'm excited to be here. It's just one of those cool things that happens in your life and happens only once."

May, ranked the club's No. 8 prospect by MLBPipeline.com, posted a 2.93 ERA in 17 starts with Rochester. He struck out 91, walked 37 and allowed four homers in 95 1/3 innings. May's 2.93 ERA ranked fourth in the International League.

May had a chance to make his debut earlier this season, but he missed nearly a month with a right calf strain sustained in late June. The injury also kept him from participating in the Futures Game at Target Field on July 13. But he returned to action July 19, and reached the 90-pitch threshold in his last outing on Monday.

"He's been doing fine," Twins manager Ron Gardenhire said. "We've been patient up here waiting for him to get here. He's been throwing good. He's excited and we're excited to see what he does."

May, along with fellow top prospect Alex Meyer, helped anchor the rotation at Rochester. And he cut down on his walk rate, which had plagued him in the past.

May has always had a power arm -- he's struck out 10.5 batters per nine innings throughout his seven seasons in the Minors -- but he has dealt with control issues. But he's cut his walk rate in three straight seasons, going from 4.7 walks per nine innings in 2012 to 4.0 last year and 3.5 this season.

May, 24, was acquired by the Twins before the 2013 season in the trade that sent Ben Revere to the Phillies. May, who will wear No. 65, was already on the 40-man roster.

May, a native of Kelso, Wash., said he'll have about a dozen family and friends in attendance at the game. He also said he's been hearing from fans on Twitter all season about when he would be called up and was excited to have it finally happen.

"I'm a pretty big Twitter guy so I see a lot of the stuff and I'm tagged in a lot of it," May said. "So I think it's fun. I think it's what Twitter is for. It's for the fans to get excited and feed off each other's excitement. It gets me excited, as if I need to be more excited. So I'm glad to have the support of the fans."

Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.