Left guard Alex Boone's right knee injury is not believed to be serious, but it likely will sideline him for the last three games of the season, a league source confirmed Monday. Second-year player Marcus Martin filled in for Boone after the injury occurred Sunday in Cleveland, and he is first in line to take over at guard the rest of the season.
Jim Tomsula said Monday the 49ers were awaiting results of an MRI at Stanford Hospital. Bleacher Report was the first to report that Boone had suffered a minor tear of his MCL, a multi-week injury but one that does not require surgery.
Boone, 28, is scheduled to be a free agent in March and likely will get plenty of attention at guard and possibly tackle, which he played at Ohio State and early in his career with the 49ers. That means Martin, who started the team's first 13 games at center, essentially will be auditioning for the role of left guard next year.
Martin and Daniel Kilgore, the team's 2014 starting center, alternated at center early on against the Browns. When Boone left the field, Kilgore took over at center and ended up playing 42 snaps.
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"He did a lot with them," Tomsula said of Kilgore's snaps. "He did. So, there was a positive there.”
The 49ers have three other young interior offensive linemen on the team: Jordan Devey, Ian Silberman and Brandon Thomas.