The 23-year-old has only scored three goals in 30 appearances in all competitions since joining in a club-record £40m deal from Hoffenheim.
"He's had a bit of a sore thigh all week so we expect him to train," Bruce said.
"As always we've done as much as we possibly can, you can put on as many finishing drills and training ground exercises as much as you want. Unfortunately Joe will be measured by one thing - goals.
"I have to say his team play, his work rate and attitude [is good]. With that I'm sure he will come good, he's still only 23."
He added: "He'll learn from what has been a difficult first half of the season for him. As long has he keeps working hard and shows the right attitude, we are convinced that we have a player in there."