The 23-year-old has missed the last four Championship games, as well as the FA Cup fifth-round tie against Chelsea, after damaging ankle ligaments in the 4-1 defeat at Crystal Palace on February 16.
He will not be available for Saturday's trip to Bristol City, nor any time soon, but Mowbray is keeping his fingers crossed that he could yet have a role to play as Boro attempt to re-ignite their promotion drive.
He told the Evening Gazette: "He played on with the injury a little bit at Palace. Adrenaline gets you through, but he's got ankle ligament damage.
"He's had a rough season in terms of injuries. I couldn't give an exact time when he will be back, but it will be weeks rather than days."