LAKE FOREST, Ill. -- The four-year, $14 million contract the Bears gave running back Michael Bush in the offseason seems like a wise investment now that starter Matt Forte is dealing with a right ankle sprain.

With Forte sidelined in practice this week after injuring the ankle against the Green Bay Packers, Bush is preparing to make his 20th career start on Sunday against the St. Louis Rams. He spent the first five years of his NFL career (Bush did not play as a rookie in 2007) in Oakland where he rushed for 2,642 yards and 21 touchdowns, while also catching 91 passes for 879 yards and a score. He rushed for 977 yards last season and became the Raiders’ featured back when Darren McFadden was injured.

Bush leads the Bears with 26 rushing attempts and two touchdowns scored in short-yardage situations through two games this season.

Talking that all into account, Bush doesn't believe Bears' fans should be shocked by what he is able to accomplish on the field Sunday against the Rams.

"There ain't nothing to show. I've already done it," Bush said. "There ain't nothing to show. I'm in my fifth year now. You guys saw me backing up McFadden (in Oakland) when it was my turn to play. I did what I was supposed to do. It might come in different ways, but I'm getting the same type of production. It's football."

Forte is able to beat teams in several different ways. He ranks fourth in Bears franchise history with 6,418 all-purpose yards, fifth in rushing yards (4,344) and fourth in receiving yards by a running back (2,074). And he has compiled 12 games with 150-plus scrimmage yards, second only to Hall of Famer Walter Payton.

Bush said he doesn't expect the coaching staff to alter the game plan much, if at all, when he is in the backfield instead of Forte.

“They told me when I came here that nothing was going to change, that they were looking for a guy to keep the offense rolling when (Forte) was out,” Bush said.