The San Francisco 49ers will be without All-Pro inside linebacker Patrick Willis (toe) and starting left guard Mike Iupati (concussion) for Sunday night's game at the Denver Broncos, the team announced Friday.

San Francisco 49ers linebacker Patrick Willis has been ruled out against the Broncos this Sunday with a toe injury. AP Photo/Billy Hurst

Willis, who was still wearing a walking boot on his left foot Friday, was injured in the first half of the 49ers' victory at the St. Louis Rams on Monday night. Willis said he jammed his foot into the artificial turf while pursuing a running back.

Iupati suffered a concussion in the second half.

Rookie third-round pick Chris Borland is in line to start for Willis. Joe Looney will take over for Iupati.

"He is pretty short, but the little dude's got a lot of fight in him," cornerback Perrish Cox said of the 5-foot-11 Borland this week. "He can tackle and he's got moves that a lot of our linebackers don't really do besides NaVorro Bowman. We saw a couple in the last game and, like I said, he's the heart of our defense right now. He'll make the calls and we've got to roll with him.

"We all got trust in Chris Borland. He's got big shoes to fill."

With Willis out, three of the Niners' four starting linebackers are sidelined with Bowman still recuperating from the devastating left knee injury he suffered in the NFC title game in January and Aldon Smith serving his NFL-mandated nine-game suspension.

Dan Skuta, who has been starting in place of Smith, said Borland has been taking tips from Willis and Bowman all along.

"He's got a unique style, different than I've ever seen," Skuta said of Borland. "He's really nifty, I think, is a good word for Chris, the way he flies around, going around blocks and everything. But he does a good job of playing physical at times, too."