After coming off the disabled list, Villarreal pitched twice for Pawtucket, converting one save and not giving up a run.
"Given what we've gone through the last couple of nights out of the bullpen, we needed a guy that had some ability to pitch a couple of innings -- a fresh arm," said manager John Farrell. "Villarreal over the last couple of outings at Pawtucket has started to throw the ball consistent with where he was a couple of years ago. The thumb issue he dealt with in the past is behind him. It's a power arm that's got some success in the big leagues."
To make room for Villarreal, Rubby De La Rosa was sent back to Pawtucket.
"Rubby going down is more a matter of getting a fresh arm here," said Farrell.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.