Guillen, the right fielder and No. 4 batter, had played just three games in the Cactus League before flu stopped him a week ago.
In his first at-bat against the Milwaukee Brewers, Guillen hammered an RBI single to left field against left-hander Manny Parra. In his next two at-bats, Parra struck him out, the last time with the bases loaded. Guillen left the game after four innings.
"His color looks better, his face looks better, he's smiling," manager Trey Hillman said. "The other day [Tuesday] he just needed another day to flush out his system. He just wasn't feeling too good."
Guillen reported to camp as scheduled on Feb. 19, but was given latitude to set his own pace of playing in games. He didn't debut until the 11th game and, after going 1-for-8, he was bitten by the flu bug.
Grudzielanek, who has a mild back strain, and Olivo, who has a groin pull, worked out on Thursday, but were held out of the game.
"We want both of those guys to get out of the night air, simply because of it being muscular, and I don't want them to stiffen up after this workout," Hillman said.
Olivo and Grudzielanek are scheduled to play in a Minor League game on Friday. If that goes OK, they'd probably play on Saturday against the San Diego Padres.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.