Cubs right-hander Mark Prior went back on the 15-day disabled list Friday, this time with a strained left oblique muscle. He got hurt while taking batting practice last Saturday in Milwaukee. Prior, who began the season on the disabled list with a sore shoulder, came off it June 18 and went 0-4 in four starts with a 7.71 ERA. He was scratched from his start last Sunday. How long will the Cubs be without Prior? "We're not sure," manager Dusty Baker said. "He was better yesterday."