CHICAGO (AP) — Carlos Zambrano visited the Chicago Cubs' team orthopedist Wednesday to check out his right arm but didn't have an MRI.

Zambrano left his start Tuesday night against the Houston Astros after five innings and 86 pitches, telling pitching coach Larry Rothschild he didn't feel well and couldn't continue, manager Lou Piniella said Wednesday.

Zambrano was scratched from his scheduled outing last Sunday and moved back two days to rest what had been described as a tired arm. But apparently his arm might be more than just weary, and he went to see Dr. Stephen Gryzlo on Wednesday.

"He visited Dr. Gryzlo this afternoon and he physically examined him. The MRI he was supposed to take, he didn't take for whatever reason, so the examination is incomplete. Until he gets an MRI done, we don't have anything to report," Piniella said.

"He was supposed to take an MRI today. It was available to him and he didn't take it today. That's it. And that's what I get from our medical people."

Piniella added that Zambrano would probably have the MRI on Thursday.

"I haven't seen Carlos. He was not here tonight," Piniella said after a 4-0 loss to Houston, Chicago's season-high fifth straight defeat.

Piniella also revealed that right-hander Rich Harden, who is being given 12 days between starts to rest his arm, has experienced some soreness.

"No, I don't think he has a tired arm," Piniella said. "He's had some discomfort, also.

Harden, who last pitched Friday against the Philadelphia Phillies, isn't scheduled to pitch again until Sept. 10 in St. Louis. He's been on the disabled list six times in his career.

"They were planning on skipping me even before I came here and it just seemed like a decent time," said Harden, 4-1 with a 1.50 ERA and five double-digit strikeout games in nine starts with Chicago since being acquired in a trade from Oakland. "I've been feeling pretty good, but I guess I've had a little bit of discomfort you could call it. But nothing serious."

It's a critical time for the NL Central leading Cubs to be worried about sore arms on their pitching staff, especially Zambrano and Harden. Sean Marshall will move into the rotation and take Zambrano's scheduled start Sunday in Cincinnati.

Piniella said the Cubs would have not let Zambrano start Tuesday night against the Astros if they thought he was hurting. Zambrano, who signed a five-year, $91.5 million contract extension last August, is just 1-1 over his last six starts and has gone past the fifth inning just twice. He was on the disabled list in June with a sore shoulder.

"Obviously you're concerned. I mean he's a top-notch pitcher, but believe me we sent him out there yesterday thinking that he was perfectly fine to go out. If not we wouldn't have sent him out," Piniella said.

Zambrano (13-5) gave up five hits and three runs with three walks in his five innings Tuesday night while getting a no-decision.

"I thought he was throwing the ball fine. The location was not really all that good," Piniella said.

"He was out there competing and it sort of surprised me in that bottom half of that fifth inning when he told the pitching coach that he wasn't feeling well and he couldn't go farther. Outside of that, I don't know anything because I haven't talked to him. ... I'd like to have clarification myself, I'll be honest with you."

Zambrano was not available for comment before Wednesday night's game against the Astros.

The Cubs called up right-hander Kevin Hart from Triple-A Iowa to help out in the bullpen with Marshall going into the rotation.