Luke Shaw has vowed to improve and admitted he is yet to hit top form at Manchester United.

The £27million defender has struggled to adapt since his summer move from Southampton.

United boss Louis van Gaal criticised his fitness levels in the summer and gave him his own training plan - something Shaw said he was right to do.

The 19-year-old, who played in United's 2-2 draw at West Brom on Monday, has given an honest assessment of his start at Old Trafford.

He said: "They haven't seen the best of me yet. I know I haven't been up to my full potential. I am trying hard and getting used to everything.

"When you come to a club like this it's never easy for a young player like me. But I'll get myself started soon and put in good performances.

"I wouldn't say I've been horrendous, but can do much better. I need to do better. I've come to Manchester United and I know what they need. I've been working hard and the performances will come."

Shaw played for England in last summer's World Cup, but dropped back to the Under-21s this month to help them qualify for Euro 2015.

He felt playing two games against Croatia was vital to boost his fitness.

"It always helps and the main thing for me was it was two 90 minutes for fitness.

"I feel fit but, like I said, I haven't played my best recently," admitted the left-back.

"That's football. Hopefully I'll come out of it now.

"I think I could still get a bit fitter from working hard in training. But I do feel pretty fit in training."

United host Chelsea in the Barclays Premier League on Sunday already 10 points behind Jose Mourinho's leaders.