A 49ers defense that's already missing a number of starters could be significantly thinner Sunday when it travels to play Peyton Manning and Broncos.
Patrick Willis left Monday's 31-17 win over the Rams in the second half with turf toe, an injury that has kept starting corner Tramaine Brock out of action since the first quarter of the season opener.
The prognosis of Willis' injury is unknown. He will undergo tests Tuesday when the 49ers return to Santa Clara, but there's a good chance the seven-time Pro Bowler will not be available against Denver. Willis was seen wearing a walking boot on the sideline after coming out of the game. The 49ers get their bye after playing the Broncos on the short week.
Willis was one of four 49ers to sustain injuries Monday. Rookie nickel back Jimmie Ward left the game with a quad injury in the second half and did not return. The extent of his injury is unknown. Left guard Mike Iupati suffered a concussion late in the third quarter and must pass the league's mandatory concussion protocol before he can play.
Wideout Stevie Johnson took a knee to the hip area when he recovered the Rams' onside kick in the fourth, but told reporters after the game he expects to recover in time to play the Broncos.
Willis' absence means San Francisco would employ Michael Wilhoite and rookie Chris Borland as their starting inside linebackers against Manning, who is three touchdown passes away from breaking Brett Favre's record of 508. He is second in the NFL with 15 TD throws this year.
Wilhoite made his eighth NFL start Monday, while Borland, a third-round pick, made his NFL debut on defense after getting all his snaps on special teams. Borland received 148 defensive snaps in the preseason, including 46 against the Broncos.
Borland played well in Willis' place in the second half Monday, making two tackles and breaking up two passes against the Rams and quarterback Austin Davis. Fellow rookie Dontae Johnson, who came in to play left cornerback when Perrish Cox moved to nickel to replace Ward, sealed the game with a 20-yard interception return for a touchdown inside the final minute.
The Broncos (4-1), own the league's third-ranked scoring offense (29.4 points per game) and fourth-best passing attack (297.8 yards per game) headed by Manning.
If Willis cannot play, he will be the third 49ers All-Pro linebacker on the sideline, joining NaVorro Bowman and Aldon Smith. Bowman is eligible to return to practice this week after starting the year on the physically unable to perform list after suffering his knee injury January's conference title game, but is unlikely to rejoin the team until after the bye week. Smith has three games remaining on his nine-game suspension for violating the league's personal conduct and substance abuse policies.
Brock has not practiced since suffering his toe injury in Week 1's win over the Cowboys, and appears unlikely to return before the team's bye week. The same can be said for right tackle Anthony Davis, who missed his fifth start Monday, after he sprained his left MCL in Week 4 against the Eagles.
Tight end Vernon Davis returned to action after missing last week's game with back spasms. He had three catches for 30 yards and a pair of drops.
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