Grove was injured late during Tuesday's practice and was not on hand for the final workout of training camp.
Shell originally indicated to reporters that Grove would have to undergo surgery but a team spokesman later said that no decision on that had been made yet. Grove is expected to have the MRI some time on Thursday.
''It's a hell of a curveball,'' Shell said. ''That's a bad thing. But, you know, these things happen. It's unfortunate that they do happen. He's a great guy, a great player and he'll be back. His teammates just have to rally around each other and trust each other. Whoever fills in will do a good job for us.''
Temporarily, at least, that job belongs to fifth-year offensive linemen Corey Hulsey, who had been working at primarily at left guard during camp.
Hulsey started at guard in Oakland's 23-7 preseason win over San Francisco on Sunday and did get some time at center during the Hall of Fame game against Philadelphia.
''I've played center enough in my life to where it's comfortable enough,'' Hulsey said. ''It's definitely going to be an adjustment. Now you have to direct the line, you're making he calls and then you have to snap the ball.
The Raiders opted for Hulsey over veteran long-snapper Adam Treu, who has filled in as a spot-starter at center throughout his 10 NFL seasons. Oakland also has rookie Chris Morris, a seventh-round draft pick this year, on the roster.
Hulsey admitted to being surprised to find himself with the starting offense on Wednesday rather than Treu.
''Because that's what I thought it was going to be,'' Hulsey said. ''Then they gave me the call. I'm happy so I'm going to go with it.''