SANTA CLARA – DeShaun Foster appears to be on the verge of his biggest game with the 49ers, but on Thursday you would have needed a polygraph to detect an extra pulse of excitement from the seventh-year tailback.

"I'm just a low-key guy," Foster explained, his voice barely audible in the din of the NFL locker room. "It's Thursday. There's no reason to be rah-rah today. … Game day's different."

Game day in fact could be very different for Foster, who signed a one-year deal with the 49ers in the offseason.

Before Frank Gore injured his ankle early in the third quarter Sunday, Foster had received 21 carries to Gore's 229. Foster has had such few opportunities, he's strained to make the most of the ones he's had. Earlier in the week, coach Mike Singletary said the running back has been too eager at times.

"The thing that DeShaun really runs into is he's trying to get extra yardage," Singletary said. "He's trying to make something happen. Frank Gore is in all the time. And then DeShaun gets a chance and he wants to show, 'Hey, I can do this. I'm a good back. I can make things happen.' "

Foster acknowledged he has tried too hard at times this season but said that shouldn't be a problem Sunday against Miami.

"You don't know if that's your last carry or not, so you try to make something happen," he said. "But going into this game, I know I'm going to get a few (carries), so I'm going to let the game come to me and play football."

Gore, meanwhile, has ditched the crutches he needed earlier in the week, but he was still walking gingerly Thursday.

He insisted, however, he still had a chance to play Sunday in Miami.

"No, not at all," he said when asked if he had been ruled out of the game. "I'm taking it one day at a time. And every day I'm getting better and better. So I'll just wait for Sunday and see how I feel."

Last year Gore sprained his right ankle in a Week 7 game against the New York Giants. He played the following week against New Orleans but had to sit out the next game against Atlanta. Gore said Thursday that the recent injury felt the same as last year's.

Gore has extra incentive to play against the Dolphins. Not only is he 22 yards from becoming the first 49ers running back to have three consecutive 1,000-yard seasons, Sunday's game would be the first NFL contest he's played in his hometown.

"It's very tough," he said. "It's not just going down (to Miami) but playing the game, period. I want to be out there with my teammates. … We're on a roll."

Tight end talk – Tight end Vernon Davis doesn't anticipate a lot of encounters with Miami linebacker Joey Porter, who tends to line up on the weak side of the offensive line. But if they do tangle, Davis said he won't be intimidated by Porter's league-leading 16½ sacks.

"I've gone up against the best," Davis said. "I'm pretty sure I've gone up against a lot of other linebackers/d-ends who were better than him. And I pretty much won every battle."

Porter is known as much for his trash talking as he is for his pass-rush moves. Davis, meanwhile, has been a frequent target of on-field barbs, especially after Singletary famously booted him from the Oct. 26 game against the Seahawks.

"That's fine. (Porter) can talk as long as he wants," Davis said. "I'm not going to let that get to me. I've talked to coach Singletary numerous times, and we have an understanding that I won't let anybody get under my skin."

Read Matthew Barrows' 49ers blog at www.sacbee.com/blogs .