Arsenal legend Martin Keown says Louis van Gaal "killed" Manchester United defender Luke Shaw by claiming he was not fit before the start of the 2014/15 season.

The 20-year-old arrived at Old Trafford from Southampton last summer in a deal worth to be £27m ($42.1m), according to BBC. In his debut season, the left-back started in only 15 league games as injuries and form forced him to miss most part of last season.

The former Barcelona and Bayern Munich manager criticised Shaw and had urged the England international to work on his fitness in July 2014. The former Gunners defender urged Van Gaal to give the United defender a chance to prove his worth.

"Van Gaal killed him a bit last season by saying he wasn't fit. He's a young boy and impressionable. He has to be given a chance to prove himself," Keown told

Shaw has worked on his fitness and is hoping to impress the Dutchman. The Mirror reported the former Saints full-back had lost three kilos through an intense tailor-made conditioning and fitness regime programme this summer.

He has already impressed during the pre-season tour and Van Gaal confirmed Shaw will start against Tottenham Hotspur in the opening match of the season on 8 August. Van Gaal is also happy with Shaw's progress and has backed him to have a big season at Old Trafford.

"Luke Shaw is a big talent. He's very young so it's not so easy for him to come from Southampton to as big a club as Manchester United," Van Gaal said, as quoted by the Manchester Evening News.

"But he has the benefit that he's an Englishman. (Memphis) Depay is a Dutchman and it's a different culture, a different rhythm to the game."

"So I think that it shall be the season of Luke Shaw, that I believe. I believe in him and he has to feel that and I hope he shall show it. But he's 20-years-old. How many players of that age are playing in the Premier League?"

Meanwhile, Keown did not shy away from praising Van Gaal for revitalising Chris Smalling's game my making a tactical change.

"Switching him from the left to the right side of defence has been critical because he needs to be on his right foot in possession. If he's not it affects his whole game. Towards the end of the season he played for England on his left side and I saw the same old indecision return," the Arsenal legend explained.