Guillen said he had a big knot in the area between his neck and his right shoulder.
"It's been bothering me for two days," he said. "They tried to dig in there yesterday, but it just got a little worse."
Guillen doesn't know how the injury occurred, perhaps just through the wear and tear of playing.
"It's behind the muscle, right in the back," he said, motioning behind his right shoulder. "I've been having some treatment and stuff, trying to get it down, but the swelling hasn't gone down."
Guillen speculated that he might even get the area loose and be able to play in the late innings against the Mariners, his club last season.
"You know how I am, I'll probably be in there later on in the game. I hate to be on the bench, especially against my old team," he said.
Designated hitter Billy Butler replaced Guillen in the cleanup spot of the lineup. David DeJesus shifted from center field to left and Joey Gathright was added to the lineup in center.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.