"It went without warning or anything," said Crain, who's wearing a protective boot on his foot. "It felt like I got hit by a ball. I thought someone threw something at me at first. I realized it was my calf. Hopefully, it was just a strain, but we'll see what the doctor says tomorrow."
Minor Spring Training muscle injuries are nothing new to Crain, who had a groin strain and oblique strain last spring. Crain has yet to throw off the mound and is recovering from biceps tendon surgery.
"Obviously, at this point, I don't want it to happen, but it's nothing I'm worried about," he said. "We're going to dictate our throwing program around it. Today, I threw off a knee. We're able to still get work in, so I'm not losing any ground in that sense.
"I always say things happen for a reason, and hopefully this will be something that doesn't cause me to rush back. I don't know what the prognosis is going to be. As long as I can get some throwing in, it won't set me back at all."
Crain was an All-Star in 2013, posting a 0.74 ERA in 38 games with the White Sox, striking out 46 and walking only 11 in 36 2/3 innings -- including a 29-inning scoreless streak. He didn't pitch after being traded to the Rays on July 29 because of the injury.
"He came in feeling better this morning," Astros general manager Jeff Luhnow said. "It was sore, so we're going to modify his throwing program a little bit in light of that. We'll know more information the next couple of days, but that will be some sort of setback. We'll continue to try and get him to work on his arm strength, but we'll keep the calf injury in mind."
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.