Bergwijn received online abuse from Spurs fans after he missed two gilt-edged chances in the recent defeat at Liverpool and he was again wasteful in Saturday's 3-0 win over Leeds.
He has yet to find the net in 11 Premier League games this season, but Mourinho says he has been hampered physically.
"We need him to score goals. Of course we know he has the ability to do that," the Portuguese said.
"If you go back one year, his first match and he scored an amazing goal (against Manchester City). We know that he has the ability to do that.
"He's accumulating also physical problems. I don't know if you could see but even in the last 10 minutes he was touching his groin, he was touching his adductor.
"He's having problems that are stopping him now and again from training properly and at high intensity so he's suffering a little bit.
"But of course he gives very good things to the team. I believe the goals will arrive if his condition improves."