In the same week that Kevin Thomson underwent surgery on the aggravated fibula he fractured earlier in the year and Andy Halliday suffered an ankle problem, Steele broke the scaphoid bone in his wrist during training.
It means the England Under-21 international has to remain with Thomson and Halliday in the North-East for treatment as the rest of the Boro squad head for a training camp in Slovenia.
Dutchman Marvin Emnes who is still being courted by Swansea City has also stayed behind nursing a slight groin problem. That he has not travelled is not, the club insist, related to Swansea's interest.
Steele suffered the break when he attempted to thwart Leroy Lita in a one-on-one encounter at Rockliffe Park.
He will see a specialist to determine whether or not he needs surgery that would require the use of metal implants, but either way the problem will need plenty of time to make a full recovery.
Middlesbrough manager Tony Mowbray will make sure his No 1 receives the best possible attention, but experts claim that such breaks can take up to six months to heal.
It is likely Mowbray will now be looking at the transfer market in the hope of bringing in a keeper on loan for the first few months of the season. Nottingham Forest's Paul Smith, who was on loan at the Riverside for part of last season, is an option.
Teenager Connor Ripley was called up to the squad yesterday to travel to Slovenia as back-up to Danny Coyne.
Coyne is likely to start against BB Istanbul tomorrow, while Middlesbrough are also due to play Antalyaspor and NK Varazdin before returning after the eight-day break next week.
Merouane Zemmama will also not be on the flight after problems with his visa, while French trialist Maloury Martin is expected to join up with the group on Saturday.
Didier Digard has sealed his back to Nice.
He had 12 months remaining on his contract at the Riverside, but he has agreed a deal that sees the remainder of his £2m-a-year terms come to an end.
A statement from Nice, where Digard was on loan last season, read: An agreement in principle was reached with the player and his club Middlesbrough. The player has arrived in Nice, will train with the group and the formalisation of the transfer is scheduled for Tuesday afternoon.
Thomson, meanwhile, underwent surgery on Monday and early estimations are that he could return to action in October.
The Scotland international returned to training 12 days ago on crutches after suffering a negative reaction to his troublesome fibula while running ahead of his return to pre-season training.