Still, Iupati will not need surgery and the injury is not expected to end his season. In last year's game against the Saints in New Orleans, the 49ers lost both running back Kendall Hunter (Achilles') and receiver Kyle Williams (ACL) for the season.
Iupati was one of the top guards in the league a year ago and was named to both the Pro Bowl and All-Pro team. He had surgery on his shoulder in the offseason and has been battling an array of issues — including shoulder and elbow injuries — this season. He briefly left last week's game against Carolina with a knee injury but returned to the contest.
There are three grades on MCL sprains, each requiring a longer recovery period. Running back LaMichael James, for example, suffered a Grade 2 sprain in late August and missed a month.
Coach Jim Harbaugh on Monday said he thought Michael Crabtree "was close" to returning to the playing field but said "we'll see" when asked if the receiver would play against the Redskins. Crabtree did not practice with the team last week, an indication that his playing debut probably is not imminent.
The team signed rookie cornerback Dax Swanson to the practice squad. Swanson originally signed with the Colts following the 2013 draft. The 49ers had an open practice-squad spot after tight end Derek Carrier was elevated to the 53-man roster Saturday.
Harbaugh did not have an update on injured starting cornerback Tarell Brown, who left Sunday's game with a rib injury. If Brown can't play, Tramaine Brock would start in his place and Eric Wright would fill in in nickel situations.