The 20-year-old, who can also play on the wing, has signed from Scunthorpe until January after finding first-team chances hard to come by at Glanford Park.
Hill said: "Bobby's a player we've admired for quite a while. He's been involved for Scunthorpe this season, albeit mainly off the bench.
"It's not one I'd expect to be able to make permanent, because he's highly regarded at Scunthorpe.
"They've let him come to us because he's not getting much football and he wants to play."
Hill has no injury or suspension concerns to contend with as his side bid to bounce back from last weekend's defeat at Sheffield Wednesday.