Manchester United forward Alexis Sanchez has conceded that time is running out for him to prove himself at Old Trafford.

The Chile international has struggled for form and fitness since joining from Arsenal 13 months ago as part of a swap deal involving Henrikh Mkhitaryan.

Sanchez was given a contract worth a rumoured £500,000 a week to join United over rivals Manchester City, but he has failed to replicate his personal success from Arsenal during his time in Manchester, scoring just five goals in 37 appearances.

Having produced another underwhelming display when called upon from the bench in the 2-0 loss to Paris Saint-Germain earlier this week, the 30-year-old admits that he is 'worried' about his future.

"I think a player like me has to show it right now. There is no time [to lose], nothing," he told the BBC Sport. "It worries me. I believe in what I am because it's game over for a footballer who no longer believes in his ability but at the same time I'm hard on myself too.

"I want to play. I want to get at defenders. I am used to playing and have had to adapt to playing 20 minutes and training at home to be physically right. I have to do it myself and be professional.

"[Ole Gunnar Solskjaer] hasn't spoken to me a great deal about what I have to do on the pitch, but I think I'm an experienced player and I think I know what I need to do and what I shouldn't do. I'm a player that, if I'm not in contact with the ball, I lose that spark, and sometimes I want to play in every game.

"You're in, you're out, and I'm used to playing. It's not an excuse because if I go on for 10, 20 minutes, I have to perform because that's what I'm here for, to make a difference. I would like to have brought more joy to the club. Yes, it worries me because I believe in my abilities as a player, I want to show it."

Sanchez, who has also previously represented Udinese and Barcelona, is in contention to start United's FA Cup fifth-round tie against Chelsea on Monday.