San Francisco 49ers offensive right tackle Mike McGlinchey underwent arthroscopic surgery on his left knee on Wednesday, coach Kyle Shanahan told reporters.

Shanahan said McGlinchey will miss four to six weeks.

McGlinchey was injured during Monday night’s 31-3 victory over the Cleveland Browns.

The injury leaves San Francisco without both starting tackles. Six-time Pro Bowl selection Joe Staley broke his left fibula against the Cincinnati Bengals in Week 2 and is expected to be sidelined for another month.

Shanahan said that Daniel Brunskill will start at right tackle and Justin Skule will continue to line up at left tackle for Sunday’s game at the Los Angeles Rams.