McManus last played for Boro back in October during their win at Watford, but soon after that he was loaned to Bristol City.
He returned to the Riverside after his spell at Ashton Gate and was on the bench for their loss to Crystal Palace at the weekend.
With Jonathan Woodgate and Seb Hines sidelined, George Friend was switched from his usual left-back position at Selhurst Park but, with four goals conceded, Mowbray could bring back McManus for their match with Burnley on Tuesday.
"Stephen was at Palace sitting on the bench, so let's see what happens," said Mowbray.
"If we need Stephen, we'll have to do what we need to do. Centre-halves have got to play in their position, so if Stephen's required, he'll play."
Mowbray did not shy away from the fact his defence has been alarmingly poor in recent weeks.
"It's becoming a concern," said the Boro boss. "To lose three at Derby, four at Ipswich and then four again at Palace, it's a worry.
"Yet there are personnel reasons. I could give you our first-choice back four, and at the minute, you'd have to say that three of them aren't playing. That's football and you have to get on with it. The squad is only ever as strong or as weak as the numbers underneath what you would call the first XI. That's what football is.
"If we've got Hoyte, Woodgate and Hines injured, you have to take it on the chin and get on with it. Unfortunately, I don't think any of them will have a chance for Tuesday."