Giambi, utilized on Saturday as New York's designated hitter, flew out to left field and walked against Rays starter Edwin Jackson before Wilson Betemit replaced him as a pinch-hitter for the fifth inning.
"It's so early in the season, a little bit cold and me DH-ing," Giambi said. "We just said, 'You know what, let's go in there and make sure it's OK.'"
Giambi said he received treatment in the Yankees clubhouse during the game, including ice. He said the condition had improved and that no further tests had been immediately scheduled.
"It's part of the game," Giambi said. "I just kind of overextended. I'm being cautious about it because it's so early. I wanted to make sure I didn't turn it into anything.
"That's why I said something about it today. I'm not going to go that route and just keep playing beat up. That's not going to get it done, either."
Giambi, 37, has been drawing regular duty as the Yankees' starting first baseman this season, batting .083 (1-for-12) with a double and two RBIs in five games.
Giambi struggled through an injury-marred 2007 campaign, but spoke optimistically about how an improved training regimen would be able to keep him on the field this season. He batted .236 with 14 home runs and 39 RBIs in 83 games for New York last season.
"We'll see Jason in the morning and stretch him out to see what he can do," acting manager Rob Thomson said. "We'll evaluate him tomorrow. He told me it wasn't too bad, but he felt it a little bit."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.Less