"We feel David has got a bright future," said manager Chris Wilder of the 19-year-old forward. "There is more to come from him than supporters may have seen so far.
"He's got pace which is frightening but we need to work on his skills and his technical ability."
Wilder, meanwhile, has reportedly ruled out a third spell at Sixfields for Bayo Akinfenwa after he opted to leave Gillingham.