Cody Ross was assisted off the field after pulling up while attempting to steal second base against the Astros.
As he approached the bag, Ross' left knee buckled. He trotted past the base, and was tagged out.
The 27-year-old outfielder, who is competing for the starting center-field job, was assisted off the field by trainer Sean Cunningham and third-base coach Bo Porter. He was taken immediately to the clubhouse, where he said he hyperextended his knee. The setback isn't believed to be serious.
"My knee hyperextended when I tried to stop," Ross said. "It just kind of scared me because I blew out my ACL before [in 2003]. It didn't feel anything like that, but it still scared me a little. I could have walked off the field by myself, but Bo said, 'No, no.' I was saying, 'I'm fine.'
"I guess if you are going to come off the field, you've got to look the part."
Ross said the discomfort came on the side and back of his knee. He expects to sit out a day or two, but is confident he should be ready for Opening Day on March 31.
In 2007, Ross was hampered by a left hamstring problem, which limited him to 66 games and 173 at-bats. When healthy, Ross has been productive, as shown by his .335 average with 12 home runs and 39 RBIs a year ago.
Ross said what happened on Friday had nothing to do with his hamstring.
"I'm going to ice it today, and see how it feels," Ross said. "If it feels good tomorrow, I'll continue on with the activities. If it is sore, I'll just treat it day by day. I don't see this being at all a problem."
Ross is not planning on having an MRI exam, unless it swells up.
Ross is in the mix for the starting center-field job, along with Alejandro De Aza and Cameron Maybin.
Earlier in Spring Training, Maybin missed some time with a hamstring problem, and right fielder Jeremy Hermida is currently sitting because of a similar left hamstring problem.
With so many ailments building up, manager Fredi Gonzalez joked: "I'm almost getting immune to it.
"The preliminary reports are that he will be OK, perhaps a little hyperextension," Gonzalez said.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.