Initial indications are that the 24-year-old could be sidelined for between four and six weeks, although the full extent of the damage he suffered during Saturday's 1-0 npower Championship defeat at Crystal Palace will not be known until the swelling has subsided.
Bates has become a fixture in the heart of Boro's defence and, with David Wheater having left for Bolton and Stephen McManus a long-term absentee with an ankle ligament problem, his misfortune is particularly badly timed.
New signing Maximilian Haas, who joined the Teessiders from Bayern Munich's II team last week, could now get an earlier chance than expected.
Speaking last week, Mowbray said: "Seb Hines has waited a long, long time for an opportunity. He has had a lot of injuries and he has had some pretty good players in front of him over the years.
"Matthew Bates, playing alongside him, is the club captain, so Max will have wait his chance."
Source: PA
Source: PA