San Francisco 49ers starting right tackle Trent Brown left Sunday's loss to the Dallas Cowboys due to a concussion. He did not practice at all this week and has been ruled as questionable for Sunday's game against the Philadelphia Eagles.

"He pulled one time and you can see it on tape," head coach Kyle Shanahan said on Friday. "He got hit right in the face and his helmet came loose. You can see the helmet come right back into him. I don't know what play number it is but one that he's pulling and going to the left."

Brown exited the game two plays later and was evaluated for a concussion, which ended his Sunday. Shanahan is not optimistic about Brown's availability on Sunday against the Philadelphia Eagles.

"He's not 100-percent ruled out but I'm not planning on it," Shanahan said. "There could be something miraculous because he hasn't been ruled out yet. It's different with the O-linemen. He has been doing football stuff but he's had to do it on the side. So if he passes all of his stuff tomorrow with no symptoms, they have an impact test and do all that, then there would be a chance for us to make a coaches' decision. But he hasn't been ruled out yet."

Brown was replaced by Garry Gilliam, who is likely to start at right tackle on Sunday against the Eagles. Shanahan discussed Gilliam on Friday.

"Garry's very athletic," Shanahan said. "He hasn't played O-lineman for a very long time. He was a basketball player coming out of college. They worked with him in Seattle, got him ready and developed him to play, got a lot of playing time last year. We brought him in here to be a swing tackle for us and to compete with our guys, not knowing exactly what we had until we got to OTAs.

"Obviously, we knew a lot about Staley, saw a lot from Trent on film. Trent did really well in OTAs and training camp so, quickly, he got that job. Garry's been our swing tackle sense and he's going to get his opportunity, most likely, on Sunday."

On April 17, the 49ers signed Gilliam to a one-year offer sheet worth $2.2 million with $1.4 million guaranteed. However, it wasn't the first offer the 49ers offered him. Gilliam was reportedly offered a front-loaded multi-year deal, which he turned down. Then the 49ers offered him a two-year deal with even more front-loaded money. Gilliam declined that offer as well.

Gilliam's agent, Mark Clouser, told The News Tribune that they didn't want to give up any of Gilliam's years in unrestricted free agency. Becoming an unrestricted free agent was important to them.