Jonjo Shelvey will miss part of pre-season after picking up a summer injury training on his own.
The midfielder sat out of the 1-0 defeat against York City and is doubtful for next Friday's trip to Doncaster Rovers at the Keepmoat Stadium.
Shelvey was in the stands at the LNER Community Stadium but only because the game came on the back of a week long stay in York for pre-season training.
READ MORE: Joelinton injury latest as striker forced off
When asked about his absence, Bruce told reporters: "Jonjo hurt himself before pre-season doing running on his own.
"He hurt his calf so he’ll not be around for a while just yet."
Bruce also had to deal with an injury for Brazilian forward Joelinton after the player lasted just 18 minutes against Steve Watson's Minstermen.
Former Manchester United skipper Bruce said: "Well he wanted to carry on which tells me that it’s not that serious but it’s obviously a concern.
"We’ll not know until we scan him and give the results out in the next couple of days."
Bruce was not too worried about the defeat to York on a day when his side created more than half a dozen good chances.
He said: "Listen, we’re disappointed with the result, of course, but it’s not all about the result.
"We didn’t deserve to lose, but it just shows you if you don’t play with the intensity and the speed and the pace you normally do, then you get frustrating afternoons like we’ve just had.
"It’s all about fitness levels.
"We’ve had a really big week in terms of the levels of what they got up to, and the kilometres they’ve done, so it’s the first of getting ready for the challenge of four weeks away.
"It was a decent workout, apart from the result."
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