The Portuguese frontman has been sidelined for four matches since coming off in the 3-1 home win over Swansea City on February 23 and has had an injection this week in a bid to help ease the problem.
On the situation with Joao, Bruce said: "It is not great, but it is better news than what I thought it was going to be last week, so the specialist has said to us to leave off it for a little while and see if it settles down.
“He has had an injection, so let’s see if that does the trick.
“It’s a little bit better news than we thought it was a week ago where we thought he might need an operation and we thought he might be out for the rest of the season. So it’s a little bit of good news."
Meanwhile, Bruce, whose side welcome Blackburn Rovers on Saturday, says that he has a poser over whether to start Sam Winnall, with the forward pushing for inclusion from the off after two substitute appearances.
Bruce has also confirmed that Dutch defender Joost Van Aken is definitely out for the rest of the season following further ankle surgery.