The White Sox designated left-hander Eric Stults for assignment to make room on the roster. Stults, 32, had no record with a 2.70 ERA in two games, one of them a start.
"I was actually pretty sore on Saturday, just body-wise," Crain said after pitching two innings for the Knights. "I hadn't pitched in a game for three weeks and so when you throw in a game, it's a lot different than throwing a bullpen.
"It was good to get out there and throw again Sunday to make sure everything was good to go. I feel good, ready to go. The two outings out there showed me I was over it and didn't feel it at all."
Crain was bothered by a right oblique strain during Spring Training, but had been on the disabled list with a left oblique strain retroactive to April 21.