Raiders left cornerback Ron Bartell has a broken left shoulder blade suffered in the first half of Oakland's season-opening loss to San Diego Monday night, according to an ESPN report.The Raiders have not commented on the report, though coach Dennis Allen said Tuesday afternoon that Bartell had a shoulder injury and was scheduled to undergo an MRI exam during the day."I'm not sure the extent to the shoulder injury," Allen said at the time.The report said Bartell would not need surgery and that while the timeframe for his return is six weeks, he is hoping to return in four weeks and was meeting with a specialist.Bartell, 30, signed a one-year free-agent contract with the Raiders this offseason after missing most of the 2011 season in St. Louis recovering from a broken bone in his neck suffered in the Rams' opener.Pat Lee replaced Bartell, who was burned for long passes of 46 and 23 yards by the Chargers, and Allen said he was fine with him at cornerback, opposite Shawntae Spencer."Hey, listen, weve got NFL football players on our roster and we expect them to go out and play like NFL players," Allen said. "He went out and did a pretty good job last night against a pretty good group of receivers and a pretty good passing game."With Bartell injured, the Raiders only have four healthy cornerbacks now in Lee, Spencer, Joselio Hanson and Phillip Adams.