The Baggies boss, who faces rising pressure given his side's lowly position in the Championship following Wednesday's derby disaster against Blues, cited a hamstring strain for Bartley.
The centre-half was at fault for a couple of Blues goals and was the subject of boos from the home crowd before being withdrawn. Bruce said that call was half on the niggle and half on the fan reaction.
Diangana, meanwhile, had barely trained with a groin issue prior to the Blues clash and Bruce revealed he was in two minds whether to start the winger, who was desperate to play. Bruce felt 'in hindsight' it was a mistake including him.
It is expected that defender Martin Kelly, the recent free agent signing, will feature in the squad at Carrow Road tomorrow given Bartley's absence. Erik Pieters, who made his debut from the bench the other night, is expected to feature while fellow new recruit Tom Rogic is not quite ready.
"Yes. They'll be a part of the squad for tomorrow maybe, one of them will be, out of necessity," said Bruce when asked about Kelly and Rogic.
"We've got one or two injuries, Bartley is carrying an injury, that is why he's not travelling.
"It was a bit of both (his Blues withdrawal), I have to say. He's got a slight hamstring.
"Kyle's got to deal with it. It's never easy or nice to hear. He's an experienced pro who will have to find the fight and stomach to get over what happened the other night.
"But he's a confident individual and he's got to accept the challenge ahead of him."
Diangana was one of a number of Albion players to struggle in the midweek derby and Bruce feels the winger looked like he was not quite ready to be involved.
"Grady was carrying a knock and didn't train in the days before the Birmingham game," Bruce explained. "In hindsight, he shouldn't have played.
"The kid wanted to play, it was a derby, he's been playing well, but he was nowhere near fit – and it looked it, I'm being honest.
"That's a conversation I'll have today with him. He wanted to play. I should've made the decision, of course he wants to play, but he was nowhere near where he can be because of injury.
"He's 50-50 – I'm going to have conversation after."
The Canaries, under former Villa and Walsall boss Dean Smith, sit second in the Championship after six league wins on the spin.