Richardson did well to finish the contest but is now considered a doubt for the upcoming game against Liverpool at Anfield.
"It summed our night up," Bruce told safc.com.
"I'd made my third substitution 30 seconds before Kieran got injured.
"It's always a gamble to use all three subs but I felt I had to throw an attacking player on with us losing 2-1.
"That's the disappointing thing. I hope he's not done anything major but we will have to wait and see how bad it is."