The 22-year-old Irishman has been one of the stars of the Barclays Premier League side's stunning return to form under new manager Martin O'Neill after being handed his chance to impress.
Tomorrow night, he and his team-mates will make the short trip down the A19 for a fourth-round replay hoping to get the better of their npower Championship neighbours at the second attempt.
The Black Cats will arrive on Teesside without several key players through injury and ineligibility, although O'Neill's selection problems pale into insignificance alongside those of opposite number, who could be without five of the men who started the 1-1 draw at the Stadium of Light on January 29.
Mowbray will be forced to draft a series of development squad players into the first-team party for the game, but he will not be afraid to do so.
He said: "The team we are playing will have a classic example.
"I don't really know the history of it, other than [former manager] Steve [Bruce] will have brought the boy McClean in from Ireland, and he didn't really surface until Martin came.
"He probably saw him in a reserve match, he was perceived as a young boy, got an opportunity and he hasn't looked back.
"Some young boys at our football club who have been playing development games and not being around the team, if they get an opportunity, who's to say they don't grab it with both hands, score the winner, push themselves in for next weekend and off they go?"
Keeper Danny Coyne and striker Scott McDonald are definitely out - the Australia international could miss up to 12 weeks with a knee injury - while Faris Haroun, Barry Robson and Marvin Emnes are all being assessed ahead of the game.
Former Sunderland midfielder Julio Arca is available after suspension, but 19-year-old striker Curtis Main, who made his senior debut as a substitute in Saturday's 0-0 league draw with Crystal Palace, could be one of the main beneficiaries of the club's injury crisis.
Mowbray said: "You have got to remember, this boy came from Darlington on a free transfer less than a year ago, so we shouldn't be expecting him to pull up trees.
"He has some raw attributes that can hurt teams, as he has done in the development squad this year.
"He is almost up to a goal-a-game ratio - he is doing okay and he deserves an opportunity somewhere along the line, and yet I wouldn't want to burden him with huge expectation.
"He is just a young boy striving to forge a career for himself after the disappointment of being let go by Darlington, so we will wait and see.
"If he gets a chance, I'm sure it won't be through a lack of effort and desire if he doesn't succeed, but let's hope he can find the net if he is given the opportunity."
Boro head into the game without a win in their last five games in all competitions, and knowing they face a major fight to rectify that situation against the Premier League's form side.
Mowbray said: "It's not going to be a cavalry charge and all guns blazing and peppering their goal. It will have to be hopefully a tactically astute game where we can be mindful of their strengths.
"All over the pitch, they have got strengths at the moment, in attacking areas anyway, and so we have to try to see that off and then ask questions of them going the other way.
"Hopefully we can do that."