The England Under-21s goalkeeper last week broke the scaphoid bone in his wrist during training which prevented him from travelling to Slovenia for a pre-season training camp.
He has been pencilled in for an operation today after specialists suggested that was the best course of action if he wants to return sooner rather than later.
Middlesbrough have enlisted the best possible care for the young goalkeeper and there are hopes he will return to action within 12 weeks.
And with other medical sources suggesting it should be a six months lay off for such an injury, the success of today's operation is likely to determine just how soon he can make a full recovery.
Mowbray has been impressed by the performances of Danny Coyne in Middlesbrough's opening two matches of their Slovenia-Croatia tour and he is set to start against Turkish side Antalyaspor tomorrow.
But Steele's injury, courtesy of an awkward fall when he dived to make a save from Leroy Lita in training seven days ago, has already led to Mowbray considering moves into the loan market.
Former Boro goalkeeper Brad Jones, who moved to Liverpool last summer for £2.3m, was mentioned over the weekend, but Mowbray is likely to see how Coyne and Connor Ripley do first.
The manager knows he can ill-afford to waste the money that is made available by chairman Steve Gibson this summer, having worked hard to offload high earners Kris Boyd and Didier Digard in recent weeks.
The Teessiders finally announced the signing of French midfielder Malaury Martin yesterday. After a successful trial, the 22-year-old signed a one-year deal.
Martin showed some nice touches in Sunday's 3-2 win over NK Varazdin, which was the released Blackpool man's first game since recovering from knee trouble at Bloomfield Road.
Martin said: I am an ambitious player and Middlesbrough are ambitious to win promotion. I've signed for one year but I would like to stay longer in England with Middlesbrough.
With Martin signed and sealed, Mowbray has now made three signings this summer following the arrivals of teenage prospects Curtis Main and Luke Dobbie.
But he has warned fans not to expect a flurry of activity following the departures of Boyd and Digard, highlighting he is still not in a position to bring in more players until he has sold one.
That means Roda winger Anouar Hadouir, also wanted by Feyenoord, could decide time has run out on Middlesbrough's attempts to land him.
Mowbray said: They (Hadouir and his agents) are fully aware of how we need to sell a player, we need to create a hole in our squad and we can't do anything about it.