The striker had been training with the club to build up his fitness and the game against Northampton was his first since April 2007.
Bates was impressed with the 29-year-old and will leave Gary McAllister to make a decision on whether to keep Christie.
"I was very impressed with Malcolm Christie," Bates told the club's official website. "He's very talented, he's here on a non-contract basis, and he gave us a different dimension.
"Malcolm is keen to prove himself and we hope that when he does, he and we will sign a full contract, but that of course will be down to Gary."
McAllister accepts that other clubs may now start looking at Christie following his return to first-team football.
He said: "He's been working on his fitness at Thorp Arch and we've been looking after him. He's back on the radar for loads of other clubs, but we've got him on a non-contract basis and we're delighted."