The striker was on the scoresheet after seven weeks out due to a thigh problem to coincide with Albion halting a three-game losing run with a 2-2 home draw against Scunthorpe.
"Billy back was a massive boost for us and really made a difference - you can see why we missed him so much," said Rowett.
"You have to realise that's seven or eight weeks out now.
"If that's him at probably 60 or 70 per cent of his best, then we'll be very, very pleased when he gets back to his best.
"He's got a phenomenal scoring rate when he starts games and I think hopefully that'll be the start of a run of games and a run of goals to lift us up the table."