Simpson is facing a spell on the sidelines after picking up a hamstring injury.
"That's the whole point of having a squad - you can't have the same 11 playing every game of the season," he told the club's official website.
"The gaffer has said that is why he strengthened the squad over the summer.
"It may be young Tav (James Tavernier), who has been around the first team for a while now and has shown in pre-season what he can do.
"Sometimes you need a chance like this to step in and try to do a good job."