Carlos Zambrano had the shortest start of his career, lasting just 1 1/3 innings because of back pain in Monday's 5-4 loss to Pittsburgh.
The Cubs right-hander, who has dealt with a variety of injuries in the past that have not prevented him from making his assigned starts, was worried enough about this injury to request an MRI, which will be done Tuesday.
If he is out for any length of time, it likely would put an end to his Cy Young Award hopes.
After Monday's loss, he is 14-6 with a 3.50 ERA.
And if Zambrano has to miss time, it's possible the North Siders will use yet another rookie in the rotation. Currently four rookies -- Juan Mateo, Rich Hill, Sean Marshall and Angel Guzman -- are in the rotation.
REPLAY: Ryan Theriot hit a three-run double in the second inning to help turn the Cubs' 5-0 deficit to Pittsburgh into a manageable 5-4 disadvantage. It looked like the beginning of a huge offensive day for both teams.
But dominant pitching took over, and the score stayed 5-4 Monday at Wrigley Field. The Cubs are 55-82 and are just a half-game ahead of Pittsburgh for fifth place in the National League Central.
INF Scott Moore, who has played third base and shortstop in the minor leagues this season, was a surprise call-up Monday. Moore might get some time as a backup for 1B Derrek Lee, who is on a program in which he takes every third game off. Moore hit .276 for Double-A West Tenn before playing one game for Triple-A Iowa.
C Michael Barrett, who went on the 15-day disabled list Sunday with an intrascrotal hematoma, is likely done for the season. He received surgery Saturday night and a draining procedure Monday morning. The Cubs already have Cs Henry Blanco and Geovany Soto aboard but may also call up Triple-A C Jose Reyes.
OF Jacque Jones left in the ninth inning of Sunday's game against San Francisco with an infection in his left tear duct. He did not play in Monday's game against Pittsburgh. Jones said he had no idea how this infection came about, but he informed manager Dusty Baker during Sunday's game that he was feeling discomfort. The Cubs hope he will be ready to start Tuesday after he pinch-hit Monday.
RHP Angel Guzman, who left Sunday's game in the fifth inning with cramps in his right forearm, is expected to make his next start, Friday at Atlanta.
RHP Carlos Marmol (shoulder irritation) came off the disabled list Monday and will report to the bullpen. Marmol had been a starter, but the Cubs felt he made too many pitches in a short amount of time due to wildness in his 15 appearances. The team wants to cut down his workload.