McKinnie arrived at camp Sunday after missing three practices last week. He was subject to a $30,000 fine each day, under terms of the 2011 collective bargaining agreement.
Coach John Harbaugh said he had "a very good conversation" with McKinnie, who attributed his late arrival to a strained back muscle.
"I didn't ask him how he did it," the coach said. "I think he said he fell."
McKinnie completed his physical Monday but did not join his teammates on the field. For that to happen, the 354-pounder has to wait for his back to heal and then pass a conditioning test.
"Like I've said many times, I think the world of B-Mac," Harbaugh said. "I do believe he's a hard worker. I do believe he's been working hard. But he's not ready to practice yet."
Michael Oher has been playing left tackle during McKinnie's absence, and there is no guarantee Oher will return to the right side once McKinnie rejoins the offense.
"My first thought right now is it's going to be a competition. We'll put the best five guys out there," Harbaugh said. "It's not ideal in the sense I'd love for Mike to be settled on one side or the other, but by the same token, that's what it is."
Copyright 2012 by The Associated Press