Michael Bush's role in 2013

Following a string of failed additions as the short-line RB in Chicago's offense -- including Chester Taylor and Marion Barber -- the Bears elected to add Michael Bush to the mix last offseason on a four-year, $14 million deal with $7 million guaranteed. Bush finished the campaign with 411 yards on 114 carries and five TDs, but his season ended early thanks to a rib injury. It has also been reported that Bush suffered a fracture in his shoulder, though he played through it. After recovering from those maladies, what will Bush's role be in the Marc Trestman offense?