The slumping Chicago White Sox made a couple of moves to shore up their pitching staff.
The White Sox also signed right-hander Freddy Garcia to a minor league deal, sources told ESPN The Magazine's Buster Olney.
To make room on the roster for Contreras, the team sent left-hander Wes Whisler down to Charlotte.
Contreras went 3-1 with a 2.70 ERA and one shutout in five starts with Charlotte after being optioned on May 10. He allowed 19 hits, walked 16 batters and struck out 27.
Contreras made his season debut on April 10 against Minnesota, just 242 days after surgery to repair a ruptured left Achilles tendon. Contreras has gone 0-5 with a 8.19 ERA in six starts with the White Sox this season, allowing 40 hits with 16 walks and 17 strikeouts.
Garcia has been battling shoulder problems for the past two years. He was released by the New York Mets in April after making two rehabilitation starts in Buffalo.
He had surgery on his throwing shoulder in August 2007 and made only 14 starts the previous two seasons with Philadelphia and Detroit. For his career, he is 118-77 with a 4.07 ERA. He made two All-Star teams.
After his contract was purchased from Charlotte on May 30, Whisler made three relief appearances with the White Sox. According to the news release, he allowed two runs. He is 5-3 with a 2.81 ERA in 10 starts with Charlotte this season.