Panthers lineman Amini Silatolu tears meniscus in practice

SPARTANBURG, S.C. -- Carolina Panthers coach Ron Rivera said after Tuesday's practice that depth on the offensive line wouldn't be a concern unless the injury news on left guard Amini Silatolu came back bad.

It's time to be concerned.

The Panthers lost their second starting lineman since training camp began after doctors in Charlotte, North Carolina, revealed that Silatolu suffered a torn meniscus in his left knee. He will have surgery on Friday, and his return timeline will be evaluated week to week.

Undrafted rookie Brendan Mahon out of Penn State will start Thursday night's preseason opener at Buffalo at what was a critical spot for the Panthers entering camp, as they attempted to replace All-Pro Andrew Norwell, who signed with Jacksonville during the offseason.

Silatolu's injury came less than two weeks after starting right tackle Daryl Williams suffered a torn MCL and dislocated patella in his right knee.

Taylor Moton, who was competing with Silatolu to replace Norwell, has been starting at right tackle since. There is no timetable for Williams' return.

"We just have some guys in the room that will have to step up,'' Pro Bowl right guard Trai Turner said.

Norwell did that in 2014 when, as an undrafted free agent, he stepped into the starting lineup and became one of the top guards in the league. That will be the challenge for Mahon, who started 41 games at Penn State.

"We kept an eye on him [in the draft], and in the end, when he didn't get drafted and we got into rookie free agency, he was our first call," Rivera said. "We got on him early and stayed on him."