Louis van Gaal has admitted that he is concerned about goal-shy Manchester United following Wednesday's fourth-round League Cup exit to Middlesbrough.

The Red Devils could not break down their Championship counterparts over 120 minutes at Old Trafford, before Wayne Rooney, Michael Carrick and Ashley Young missed penalties in the shootout.

It was United's second successive 0-0 draw following Sunday's stalemate with Manchester City, and the Dutchman concedes that he is worried about his side's profligacy.

"We have to solve this problem. We have to start finishing chances," he told reporters. "We also had more chances than our opponents against Manchester City, but you have to finish them. We now created more than against City, but you have to score.

"We had a lot of players who could have scored, but they did not do it. It is not just one player and that is a little bit frustrating.

"We are out of the League Cup, so we are all disappointed. We were really close and it is very disappointing to lose here. I am pleased with the performance of some of my players, but I am disappointed with others."

United travel to London for a trip to Crystal Palace on Saturday.