The injured knee is just the latest setback for Schilens, who missed significant time last season with a broken left foot that still hindered him early in training camp.
"I'm very concerned," coach Tom Cable said. "It's been a tough road for him. We get through the foot thing now and something else has kind of reared up on us. We'll take care of it and get him back as soon as we can."
Cable said the knee injury was likely a result of overcompensating for the foot injury. The Raiders hope Schilens will be back by the opener Sept. 12 at Tennessee if he does need the surgery.
Schilens missed the first eight games last season after breaking his foot early in training camp and was never completely healthy after his return. He had 29 catches for 365 yards and two touchdowns, but needed another operation after the season to help the foot fully heal.
The Raiders treated him cautiously early in camp this year, keeping him out of two-a-day practices and giving the foot plenty of time off because he is being counted on as a big part of Oakland's passing game.
Schilens was a seventh-round pick out of San Diego State in 2008. He has 44 catches for 591 yards and four touchdowns in his two NFL seasons. While those numbers are nothing spectacular, only one receiver on Oakland's roster has even more production. Johnnie Lee Higgins has 47 catches for 676 yards and four scores in three seasons, but is not a sure bet to make the roster this year.
Quarterback Jason Campbell completed all five passes for 89 yards on the opening drive before sputtering a bit after that. Campbell finished 10 for 20 for 170 yards with an interception.
"I'm encouraged by that group," Cable said. "Hopefully we don't lose Chaz for any time here. But if it does happen I do think we're developing that group."
Campbell also completed three passes to tight end Zach Miller and Oakland got 105 yards receiving from the running backs with a successful screen game.
"We're doing a decent job right now of executing it," Cable said. "That's exciting. We got some linemen who can run. They're getting out and getting people on the ground. The backs are making nice cuts off it and the timing by the quarterback has been good. I'm very encouraged by it. We just seem to be doing a better job of it this year thus far."
C Samson Satele underwent X-rays on his sprained ankle Monday. Satele left Saturday's game against the Bears with the injury and Cable does not know the extent of it. ... Cable expects most of his other injured players to return to practice Tuesday, including RB Darren McFadden (hamstring), DL Richard Seymour (triceps) and Heyward-Bey (fatigue). ... The Raiders have three more practices in Napa before returning to their year-round facility in Alameda prior to Saturday's game against San Francisco.