Mowbray, who will send Boro into FA Cup third-round battle with League Two Burton Albion on Saturday, has admitted he will have to sell before he can buy, and is now waiting for something to give.
Out-of-contract defender David Wheater is arguably his biggest asset with the Teessiders all but resigned to losing a man who could leave for free in the summer.
Mowbray told the club's official website: "As January goes on, managers and chief executives get lots of calls and we have discussions along the way.
"There are things under way - let's see how they resolve themselves.
"I would like to tell you more, but we have to be very professional and make decisions that suit us best as we go along. There are likely to be outgoings before any incomings."