"This is just something that we've got to do right now," Twins manager Ron Gardenhire said. "We need to make some changes. We need some hits. We need some new life in here, the whole package."
Valencia went 0-for-4 with an RBI on Wednesday to continue his recent slide, as he's hitless in his last 25 at-bats. It's been a frustrating season for Valencia, who is hitting just .190 in 27 games just two years after hitting .311 in 85 games as a rookie in 2010.
"Obviously nobody wants to get sent down, but it's hard not to say I didn't see it coming because I haven't been hitting very well," Valencia said. "I've been inconsistent. My defense has been good, but I'm a guy that needs to contribute offensively."
The Twins will use a combination of Alexi Casilla, Jamey Carroll and Trevor Plouffe at third base in Valencia's absence.
Mastroianni, meanwhile, began the season at Double-A New Britain, batting .143 with one double in nine games, before being promoted to Rochester on April 14. In 19 games with the Red Wings, he hit .346 with two doubles, two triples and 10 stolen bases.
"Mastroianni has been playing the living fire out of the game down there," Gardenhire said. "Probably the most exciting player they have on that baseball team right now, running bases, stealing bases. He can fly. We'll see. We'll see how he does."
Walters made six starts with the Red Wings, posting a 2.70 ERA with 25 strikeouts and six walks. Saturday will mark his fifth career big league start, as he has a career 7.24 ERA in 20 games with the Cardinals and Blue Jays.
"He's a strike-thrower, mixes all his pitches in," Gardenhire said. "Velocity's somewhere between 87 to 90. Very confident. They tell me he's the best pitcher available right now. He's throwing the ball very, very well."
With Walters joining the rotation, Liriano, who has a 9.45 ERA in five starts, will move to the bullpen, but his stay could be short if he starts to turn it around.
"We just gotta get him right," Gardenhire said. "We've got to get him into some situations to try and get him some success. We've talked about it. Maybe a couple innings here, a couple innings there, he blows some people away and gets some kind of mojo going. Then we see if we can get him back in there. We need him as a starter."