"I've got all the faith in the world that Tashard can go in there and get the job done," Spiller said Tuesday, after he missed practice because of sore left ankle.
Added Jackson: "He's a guy that we can lean on."
The Bills (2-2) just might have to in facing a short week of practice before playing at Cleveland (2-2) tonight.
Spiller will be a game-time decision after he hurt his ankle in the third quarter of a 23-20 win over Baltimore on Sunday.
Jackson intends to play, but he'll be wearing a brace to protect a left knee he sprained against the Ravens.
It's a familiar position for Choice, a seventh-year player -- and against the Browns, no less.
In Week 3 of last season, Choice stepped in for both Spiller and Jackson, and finished with 91 yards rushing in a 24-14 win at Cleveland.
"Oooh, it's exciting," said Choice, who is mostly used on special teams. "I try to keep it calm as I could possibly be right now. But when I'm in the game, man, I'm going 100 miles an hour."
The Bills had encouraging news on other injury fronts following practice.
Aaron Williams, who can start at either safety or cornerback, said he expects to be ready to play after he bruised his back against Baltimore.
Coach Doug Marrone listed starting cornerback Leodis McKelvin day to day after the player missed last week's game with a pulled right hamstring.
Marrone opened the possibility that starting safety Jairus Byrd could make his season debut after missing the first four weeks with plantar fasciitis in both feet. Marrone called Byrd a full participant in practice, which is a first for the two-time Pro Bowl player this season.
Byrd wouldn't characterize himself as practicing fully, but agreed he's inching closer toward playing.
"I haven't had any setbacks or anything like that, so we'll see," Byrd said. "I think it's more headed in the right direction."
As for his chances of playing Thursday, Byrd said that will be determined after he consults with Marrone.
The Bills' secondary could use reinforcements after finishing the game against Baltimore minus all four starters. That includes cornerback Stephon Gilmore, who is expected to miss at least two more games with a broken left hand.
The Bills' situation at running back is also a concern.
Spiller jogged lightly through a few individual drills, before spending time riding a stationary bike.
"To be honest, I didn't think I'd be able to run today," Spiller said. "I wasn't full speed, but I was at least able to move around."
Spiller intends to test the ankle on the field at Cleveland before the game to determine whether he can play.
Jackson was more active in practice in taking part in every drill while having his left knee wrapped.
Marrone wasn't sure of Spiller's status, but said Jackson he should be a go. If Spiller can't play, Marrone opened the possibility of promoting running back Ronnie Wingo off the team's practice squad.
The running attack has so far been the Bills strength, while also taking the pressure off rookie quarterback EJ Manuel. Buffalo ranks second in the NFL with 608 yards rushing.
Spiller and Jackson led the way over Baltimore. They combined for 164 yards rushing against a Ravens defense that had allowed just 224 yards in its first three games.
The Browns present a tough test, featuring a defense that's giving up a league-low 2.9 yards per carry.
Buffalo's ground game has Browns coach Rob Chudzinski's attention given how it ran over Cleveland's AFC North rival Ravens.
"Any time you can do that against Baltimore's defense, it's an impressive feat," Chudzinski said. "They did it and they were consistent doing it."
Choice understands it's his job to make sure the running attack doesn't miss a step if he's in there.
"You don't get many opportunities," said Choice, in his second full season with the Bills. "You've got to get in and perform. And if you perform well, they know this guy is capable. Then you get more opportunities."
AP NFL website: www.pro32.ap.org