Guillen fouled a ball off his left shin on Saturday and left one of his most productive games in the seventh inning.
"We got the ice on it yesterday, and I'm sure getting him out when we did helped reduce some of the swelling, so hopefully he'll be OK," manager Trey Hillman said.
Guillen certainly looked OK in the third inning, when he belted a two-run homer into the left-field seats against Yankees starter Joba Chamberlain. It was Guillen's 10th homer.
Guillen had a career-best seven RBIs and had two home runs among his three hits, including a grand slam, in the 12-11 loss to the Yankees. He also threw out two runners, one at the plate and one at second base.
He was switched from left field to right on Friday night to take advantage of his strong throwing arm.
Seven RBIs has been accomplished 10 times in Royals history. The last previous occasion was July 22, 2004, when Mike Sweeney knocked in seven at Detroit. The slam was the 100th in club history and the first since Sept. 16, 2006, when Ryan Shealy connected against Seattle.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.