Paddy McNair
McNair criticised after Southampton performance.Getty

Manchester United manager Louis van Gaal has explained he was left with little choice but to substitute youngster Paddy McNair before half time against Southampton because he felt the defender had lost confidence.

McNair, 19, was handed his fifth start of the season against Ronald Koeman's side but was replaced by Ander Herrera after 39 minutes.

The Northern Irish youngster made a number of mistakes in an error-strewn performance from van Gaal's side despite them claiming an unlikely 2-1 victory that lifted them to third in the Premier League table.

In his post-match interview, the United boss explained: "[McNair] had no confidence, he had given three chances away. It is very disappointing for me and for Paddy, but I had to because as a manager I am responsible.

"It is tough but it is also in his best interests. I have made a lot of changes and all the boys can survive. It is only one match, one moment in a lifetime."

Van Gaal has previously turned to McNair during an injury crisis that has crippled his defensive options this season, starting the 19-year-old in games against West Ham United, Everton, Crystal Palace, and Arsenal before Monday night.

The Dutchman has been vocal in his praise for McNair this season following his decision to call him up from the Under-21 squad for the first time.

"He was outstanding in his first match," van Gaal said of the defender in October. "You see the reaction of fans. Every time he touched the ball – applause."

United were restricted to just three efforts on goal on Monday night but still managed to secure three points against Southampton thanks to a brace from Robin van Persie. It was the club's fifth consecutive win and lifts them into the top three for the first time since August 2013 ahead of the visit of Liverpool on Sunday.