That ball that Darin Mastroianni fouled off his foot in Fort Myers did more damage to his season than anyone realized.

Mastroianni will have surgery Wednesday to repair a chip in his left ankle bone, a procedure that will keep him out of action at least until July, the Twins said Friday. The chip was detected when the reserve outfielder was diagnosed with a stress reaction in his ankle, and "when they took him out of the [walking] boot, they saw it's still there," said assistant General Manager Rob Antony. The stress reaction has mostly healed, Antony said, but Mastroianni is still bothered by the bone chip.

"In some people, this doesn't affect them at all. But with him, [the team's doctors] said it was close to the ligament," Antony said, so an arthroscopic procedure will grab the chip and reattach it to the bone. "Optimistically, [we] hope he will be back on the field in six weeks [doing] rehab."

Mastroianni originally injured the ankle during a spring training game March 28. He played eight games before going on the disabled list.

Perez released

The Rafael Perez reclamation project ended on Friday.

The Twins had a deal with the lefthander when they signed him in February: Call him up by May 1 or release him. The deadline was adjusted to sometime in June when his recovery from shoulder surgery progressed more slowly than anticipated, but the Twins determined this week, after watching Perez pitch four times for Class AAA Rochester, that they wouldn't have a roster spot for him anytime soon.

"It just didn't look like he was going to be ready to come up here and help us," Antony said of Perez, whose velocity never reached 90 miles per hour.

The former Cleveland reliever isn't the only pitcher to discover shoulder injuries are difficult to recover from. Rich Harden, still at extended spring training as he tries his own comeback, is doing "not very well, to be honest," Antony said. "He threw live [batting practice], and said his shoulder didn't feel great, so we backed him off a little bit."

Mauer has sore back

Joe Mauer woke up with a sore back Friday, and the Twins decided to take no chances with their hottest hitter. The three-time batting champion was out of the lineup, only the second game he has missed this season.

Mauer's condition doesn't appear serious, and manager Ron Gardenhire said he expected the catcher, in the midst of a 14-game hitting streak, to play Saturday.

"I think everybody's done it — you wake up and all of a sudden you can't hardly move," Gardenhire said.

The most discomfort, Gardenhire said, might not be to Mauer's back, but to the Twins lineup. Lacking better options, the manager made Chris Parmelee his No. 2 hitter, the first time in his major league career he has batted there.

"He needs at-bats," Gardenhire said. "Parm's not afraid to take pitches."

Parmelee was a leadoff hitter at Chino Hills (Calif.) High School, but said he doesn't have much experience batting second.

Etc.

• Reliever Tim Wood is in the Twin Cities to have his shoulder examined on Friday evening.

• Righthander Cole De Vries, who gave up six runs on 11 hits in four innings for Rochester on Wednesday, will make at least one more rehab start for the Red Wings before the Twins decide what to do with him, Antony said.

• Wild players Zach Parise, Josh Harding and Tom Gilbert will participate in a home run contest with TC Bear before Saturday night's game.