Boro have not kept a clean sheet in their last five games and conceded 11 goals in the process, several of them at the death, in the wake of David Wheater's departure for Bolton and Matthew Bates' hamstring injury.
They head for Reading on Saturday sitting just six points clear of the npower Championship drop zone and knowing they need to tighten up if they are to avoid the fight for survival below them.
Mowbray said: "When you look at the balance of the squad, I don't think we have a goalscoring midfield player in the squad so the balance of the midfield week in, week out has been defensive, the set-up of the team has been defensive.
"Until David Wheater left and Matthew Bates got injured, defensively we were on average conceding a goal a game and I don't think the goals against column was anything to concern me.
"Since they have been out of the team, the goals against column does concern me, of course. You can't keep losing two or three goals in every game."
Source: PA
