He passed what he called the final test by running the bases on Wednesday prior to Kansas City's game at Cleveland.
"It was good," Guillen said with a smile.
Manager Trey Hillman isn't sure if Guillen will return in Saturday's lineup against the Detroit Tigers as the right fielder or the designated hitter. He went on the disabled list on April 10 with a partially torn right hip flexor tendon.
"He hasn't had any setbacks," Hillman said.
Hillman would prefer that Guillen play right field, but that could depend on the weather. He'd hesitate using Guillen on wet grass because of the hip injury.
Guillen had played in only three games, notching two hits in 12 at-bats (.167), with no extra-base hits or RBIs.
The Royals will have to make a roster move to make room for Guillen, and Hillman said it would probably involve a position player, not a pitcher.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.