Harper hopes he, Krul and Rob Elliot will be given ample opportunity to impress over the remainder of the season, with Newcastle having to juggle domestic and European commitments.
"Tim's comeback's not too far away, but we do have a lot of games coming up," Harper told the Evening Chronicle.
"We have Robbie here too pushing for a place. He has made big strides forward in the last month or two.
"Those performances will do him the world of good."