CHICAGO -- Rookie Anthony Reyes is almost certain to start the Cardinals' game on Thursday against the White Sox at U.S. Cellular Field, but the right-hander has not officially been announced at this point.

"There's a better than 50-50 chance Anthony Reyes will come up here and pitch that game," said pitching coach Dave Duncan before Tuesday night's game. "But is it a lock yet? No."

The Cardinals have moved Sidney Ponson to the bullpen, at least temporarily, as they deal with a rash of short stints by their starting pitchers. Ponson made his first relief appearance of the year on Tuesday night after Mark Mulder endured another off night.

Following an off-day Monday, Mulder pitched on four days' rest on Tuesday, and Jason Marquis will do the same on Wednesday. Chris Carpenter will pitch on his regular rest on Friday in Detroit, with Jeff Suppan pitching on very long rest (seven days) on Saturday against the Tigers.

That leaves Carpenter on schedule to pitch in virtually all of the Cardinals' biggest series between now and the All-Star break -- against Detroit, Cleveland, Atlanta and Houston.

Manager Tony La Russa would not tip his hand on Tuesday afternoon, asserting that the Cards had four viable options for the Thursday game -- Reyes, Ponson, Suppan or a "bullpen game." However, Suppan and Duncan both said that Suppan will pitch on Saturday, and a bullpen game wouldn't make much sense for a team with an overtaxed bullpen.

That left Reyes and Ponson. And with Mulder's early departure on Tuesday night, Ponson came in to pitch in relief.

"What we're going to do is play the games tonight and Wednesday and use everybody at our disposal," La Russa said before Tuesday's game.

Reyes, fellow rookie Adam Wainwright and Ponson battled for the fifth starter's job in Spring Training, but it was essentially Ponson's to lose -- and the veteran did not lose it.

Wainwright was put in the bullpen, where he has pitched brilliantly, while Reyes headed to the Minors to start every fifth day. Reyes has made three big-league starts, two as an injury replacement and one last summer to give the rest of the rotation an extra day of rest.

Ponson started strongly but has not been sharp in recent starts. His ERA climbed from 2.81 to 4.34 in four starts after he returned from the disabled list on May 27. He missed three weeks with a tender elbow.