Manchester United vs. Middlesbrough: Louis van Gaal, Aitor Karanka Reaction

Manchester United manager Louis van Gaal conceded he is worried by his team's lack of potency in attack after watching his side crash out of the Capital One Cup at Old Trafford, losing 3-1 on penalties to Middlesbrough. 

However, Boro coach Aitor Karanka claimed his collective were the fitter unit, as the Championship contenders held United to a goalless draw over 120 minutes. 

Van Gaal spoke after the match about his pride in his players' application, but pointed out that his team missed "easy chances" in their effort to progress to the next round, per Joe Bernstein of MailOnline:

"

Of course it's a concern to miss chances. In football, the only thing that matters is a goal. We have played two matches zero-zero and could have scored in both of them.

We had easy chances in front of goal and their goalkeeper. When you don't finish them, it is very difficult to win a game.

You can say we were unlucky because we had good chances but you have to force the luck also. We didn't do that because we didn't score. But I know in football it can change.

My players have given everything and that's why I am also proud of them because until the end they have done it. Penalties is a casino—you never know.

"

Jon Super/Associated Press

United controlled the game for large periods of the night, but they couldn't convert despite captain Wayne Rooney's introduction at half-time for James Wilson. 

The Red Devils peppered the Riverside Stadium club's goal at times, but they were lacking in the shootout, surrendering 3-1 on penalties after awful misses by Rooney and Michael Carrick began the slide to defeat. 

The loss means Van Gaal's team have won only once in their five previous attempts in all competitions, according to WhoScored.com, as United's attackers appeared limp in the final third of the pitch. 

Memphis Depay was recalled to the team after being dropped by the United manager, but he struggled to make an impact before his substitution for Anthony Martial in the second half. 

Jon Super/Associated Press

Middlesbrough defended valiantly and looked dangerous on the break as they attempted to bury the ghost of last season's Capital One Cup exit—a 14-13 penalty shootout defeat to Liverpool. And Boro did just that, as they bolted the stable door and clinically finished United off when it mattered most. 

Karanka was joyous in victory, and highlighted his team's superiority in the contest, per Bernstein:

"

I told my players after the game that we were better than them—we were more confident on the pitch, we were fitter than them.

For that reason, I have to say how proud I am of my players. Penalties sometimes you lose—last season we lost against Liverpool after 30 penalties—and sometimes you can win like today.

The main thing is the performance, and the performance today against Man United, a big team, it was amazing.

"

Matthew Ashton - AMA/Getty Images

Even with United's dominance with the ball at feet, Boro certainly deserved their win despite two handball incidents being missed by the officials that should have led to penalties. 

However, the Red Devils had a host of chances to win the match, but failed to exploit the space given to them by the Championship team.

Pundit Danny Higginbotham spoke about United's failure to turn the screw on their opponents:

United join Arsenal and Chelsea in departing from the competition prematurely, and they miss out on a genuine opportunity to win silverware this term.

The League Cup has never been of high priority to the Old Trafford club, but a trip to Wembley was on the cards after the Gunners and the Blues were defeated on Tuesday.

Van Gaal fielded a strong-enough side to win on Wednesday night, but the lack of tempo will concern United supporters as there wasn't any cut and thrust from Rooney and his team-mates.

Shaun Botterill/Getty Images

Indeed, the skipper often found himself deeper than Carrick on the pitch, dropping level with his central defenders to collect the ball, nullifying his own threat. 

United are well positioned in the league table, and will lick their wounds before their tricky visit to Crystal Palace on Saturday—a match that could represent a banana skin to the team's ambitions before the Christmas period kicks in.

Van Gaal needs the likes of Rooney and Memphis to bring their best form to proceedings in the coming weeks, but if the team continue to be goal shy, November will be a difficult month for the side.