UPDATE: Iupati has been termed questionable to return and is getting X-rays for an ankle injury, per Sam Farmer of the LA Times.
UPDATE NO. 2: Iupati has now been ruled out.
Iupati got rolled up on and had to be helped off the field. He didn't put any pressure on his left leg and had to be taken to the locker room on a cart. No official word has come out on his injury, but he didn't look good coming off the field.
Iupati is arguably the 49ers' most valuable offensive lineman. He's rock solid in pass protection and a mauler in the running game. Establishing the run becomes much tougher for the 49ers with Iupati out of the game. The guard also dealt with a sprained MCL injury in December, so the Niners already have a bit of experience operating without him recently.
Adam Snyder is the next man up for San Francisco and has replaced Iupati.