CHARLOTTE, N.C. -- Starting fullback Will Tukuafu is believed to have sprained the medial collateral ligament in his left knee, and he will undergo an MRI on Monday, a league source said.
His status for Sunday's NFC Championship game is unknown, although 49ers guard Mike Iupati missed four games with a MCL sprain earlier this season.
Tukuafu did not return after injuring his knee while getting tackled on a third-down reception on the opening drive.
Tukuafu re-signed with the 49ers' last month and has served as their primary blocking back in the wake of Bruce Miller's season-ending shoulder injury last month at Tampa.
Anthony Dixon has split time with Tukuafu in the fullback role. Dixon had no carries in Sunday's 23-10 win.