Now, with starting first baseman Paul Konerko on the 15-day disabled list, Guillen isn't so sure.
Thome felt back stiffness last week in Detroit and was left out of the starting lineup for three games while he rested. That injury, combined with injuries from previous seasons playing first base, all but ruled Thome out of regular playing time at National League parks this season, including at Wrigley Field this weekend. Guillen said it would take two weeks for Thome to recover when he played first for one game last year.
That plan changed when Konerko endured a Grade 1 strain of his left oblique muscle on Tuesday. The question now is whether Thome thinks he's healthy enough to play the field.
"Right now I do," Thome said. "Last week I didn't, with that back issue. I think that's the concern, that's always been the concern.
"We haven't really sat down," Thome continued. "I know maybe there is a possibility of doing it. That's Ozzie's call. I think we'll talk more about that as we get closer to the weekend. I don't want to say yes or no, but that's more or less Ozzie's call. If need be, we'll get out there."
As Thome continues to heat up at the plate, the decision for Guillen continues to get tougher. Thome's slugging percentage has jumped 43 points in June, and he smacked his 14th homer of the season Tuesday, tying him for 16th place on the all-time list with Ted Williams and Willie McCovey.
"It depends how we hit in the next few days -- we're going to face another lefty the first day, and obviously he's not going to be in the lineup," said Guillen, speaking of facing Ted Lilly on Friday. "We'll see how we do these days.
"He'll prepare. I'm going to let him know that I don't want him doing anything at first base. Just get there and catch the ball when they throw it to you. If they hit a ground ball to you and you miss it, blame it on me."
David Just is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.