The Latics' lack of goals - they have scored only seven in 14 Barclays Premier League matches since the turn of the year - has been compounded by recent frailties in defence.
Having conceded four against both Everton and Arsenal, they also lost 2-0 against Blackburn last weekend.
"You don't have to be Einstein to work out where we are short at the moment," said Bruce, ahead of the visit of Bolton on Saturday.
"If you look at the table for goals scored, we need to improve on that. Last week in the first minute we hit the bar and in the last minute we had two off the line, it was just not going to be our day.
"But what disappointed me was we conceded against two set-pieces; although they are a big part of the game, we had tried to plan against that all week. We had enough to win the game but, always, if you don't score a goal, you leave yourself open."