The reserves crashed to their first FA Premier Reserve league defeat of the season at Kingston Park, with Darren Ambrose on target in the 2-1 defeat.
But the real bad news was the injury to Harper, which if more serious than first thought will mean Tony Caig is recalled to the first team squad.
A club spokesman said on Tuesday: "Steve Harper is having a scan today, but he expects to be out for at least two weeks.”
Last week the club allowed young gloveman Adam Collin to join Oldham Athletic on loan, which could now mean a busy couple of weeks in the two reserve teams and academy side for Ben Smith and Adam Bartlett.