Boro were hoping to have added a fresh face to their ranks prior to Saturday's 2-0 defeat at Queens Park Rangers.
They thought a deal had been wrapped up, only to see an untimely training ground injury leave them empty-handed.
It has been a case of back to the drawing board for Mowbray and his transfer plans, but he is confident business will be done during the loan window.
He told the Middlesbrough Gazette on his recent recruitment frustration: "We had a hotel room booked for a player coming in on Friday night.
"We'd agreed it with the manager, the deal was done and I received a call 15 minutes later to say they'd picked up an injury in training and the player wouldn't be coming, it would be too much of a risk to let him go.
"We had a shirt with us with the name on the back and the number registered with the FA. We might go back to them when the injury clears up.
"It's something we're trying to address. By the time the international break ends, we may have one or two new faces in."