The 24-year-old has clocked up 142 appearances since making his debut in August 2010, but he had yet to feature this season, and has figured just twice since Aitor Karanka took over from Tony Mowbray almost 12 months ago.
The Boro Head Coach signed Tomas Mejias on a permanent deal during the summer and had confirmed publicly that Steele wouldn't be figuring in his plans.
"I said if he has a good choice to go then for me it wasn't a problem," said Aitor.
"I told him one or two months ago if he had another choice he could go. He knows that he is not my first choice or my second choice."