In a 3-1 win over the Houston Astros on Monday, Maddux pitched 6 2-3 strong innings before leaving with the injury.
“I’m OK. I mean I was more tired than anything. I mean there is nothing wrong,” Maddux said after his 293rd career win.
Maddux received treatment reluctantly, according to Cubs trainer Dave Groeschner.
“We’re trying to make him a better patient,” Groeschner said of Maddux. “To him, (the muscle strain) is not a big deal.”
Maddux received heat treatment, and had no problems after a throwing session Thursday.
The Cubs are hoping Sammy Sosa’s recovery will move along as quickly. The slugger has been on the 15-day disabled list with a sprained ligament in his lower back, an ailment brought on by two violent sneezes May 16 in San Diego.
After a workout in the batting cage Saturday, Sosa said he is still experiencing pain in his back at the end of his swing. He does not have a definite timetable for his return and does not plan to rush.
“I don’t know when I will come back,” said Sosa, who is batting .291 with 10 homers and 24 RBIs.
The Cubs ended a three-game losing streak with a 6-1 win Saturday. Carlos Zambrano pitched eight solid innings and Rey Ordonez delivered a two-run single in the seventh. Derrek Lee added a two-run homer, his sixth of the season.
Pittsburgh was without manager Lloyd McClendon, serving the first of a two-game suspension for his shouting match with Cardinals manager Tony La Russa on Thursday that caused both benches to empty.
The Pirates have lost six of their last seven games.