Provided a sore right toe doesn't become any worse in the next few days, Chicago Bears tailback Anthony Thomas will put his best foot forward on Sunday, with the rookie slated to take over the starting job from James Allen against the San Francisco 49ers.

Team officials told ESPN.com that coach Dick Jauron and coordinator John Shoop will continue the rotation system employed so far this season, but that Thomas' performance against the Cincinnati Bengals last week has catapulted him ahead of Allen, and that the coaching staff hopes he can retain the No. 1 spot for the balance of the year.

A second-round choice and the 38th player selected overall in the draft, Thomas rushed for 188 yards last week, a franchise record for a rookie. The total represented the eighth-best rushing performance in Bears history.

Thomas, who is nicknamed the "A-Train," surprised even his teammates with the speed he displayed in the Chicago victory, and he could be a key player as the Bears seek their first playoff spot since 1994. Chicago, which has finished last in the NFC Central for four straight seasons, is off to a 4-1 start.

"You knew he had the power, but we wondered about his speed, could he run away from people if he got into the secondary," said offensive right tackle James Williams. "But he answered those questions last week. He got to the hole and just kept going."

The only caveat surrounding Thomas' ascension to the first unit is a sore big toe on his left foot, an injury that kept him from practicing on Wednesday afternoon. Thomas said he could have worked but team officials suggested he sit out the session. He will practice on Thursday, the former University of Michigan star said.

Thomas has started before a fullback, in tandem with Allen, but this will be his first start at tailback. Allen was the subject of some trade discussions this week, as the Baltimore Ravens inquired about his availability. Allen rushed for 1,120 yards in 2000.

In five games, Thomas has carried 47 times for 312 yards.

Len Pasquarelli is a senior NFL writer for ESPN.com.