Manchester United midfielder Ander Herrera says he is losing sleep because he fears his position at the club will be threatened when the club strengthen their midfield in the summer transfer window.

The Spaniard joined United from Athletic Bilbao in 2014 and has enjoyed the finest season of his three-year spell in Manchester under Jose Mourinho this year.

Herrera has made 42 appearances so far this season and was particularly impressive in United’s 2-0 win against Chelsea last weekend, setting up Marcus Rashford's opening goal and scoring the second, while man-marking Eden Hazard throughout the game.

Manchester United 2 Chelsea 0 player ratings Show all 22 1 /22 Manchester United 2 Chelsea 0 player ratings Manchester United 2 Chelsea 0 player ratings David de Gea - 6 out of 10 Rarely tested. Impressive under the high balls and in his distribution. Manchester United 2 Chelsea 0 player ratings Antonio Valencia - 7 Solid all round performance from him. Strong going forward and assured on the back foot. Physically impressive too. Manchester United 2 Chelsea 0 player ratings Eric Bailly - 7 COmposed under pressure, read the game brilliantly and made all the right decisions. Excellent defensive display. Manchester United 2 Chelsea 0 player ratings Marcos Rojo - 6 A gritty and fiesty display. Battled hard against Costa and largely kept his cool while the Spaniard repeatedly lost his. Manchester United 2 Chelsea 0 player ratings Matteo Darmian - 6 Kept Pedro under wraps and limited the wingers' influence for much of the game. Manchester United 2 Chelsea 0 player ratings Ander Herrera - 8 Demonstrated fantastic vision to play in Rashford for United's goal. Hard-working as ever. Shame about the yellow card but completely ran the game today. Manchester United 2 Chelsea 0 player ratings Marouane Fellaini - 7 United's battering ram. Strong in the air, firm in his challenges and excellent at breaking up play. Dominated against Kante too. Manchester United 2 Chelsea 0 player ratings Paul Pogba - 7 A rounded, mature performance from the Frenchman. May not have threatened as others did but kept the United midfield ticking over with his constant passing and movement. Still missing that 'wow' factor though. Manchester United 2 Chelsea 0 player ratings Ashley Young - 7 Another hard worker who dug deep to give 100 per cent today. Made some encouraging runs going forward and was vital in the build-up to United's second. Manchester United 2 Chelsea 0 player ratings Marcus Rashford - 8 FUll of confidence and energy. Used his pace to devasting effect and proved to be too much for the visiting defence at times. Showed today what he's truly capable of. Manchester United 2 Chelsea 0 player ratings Jesse Lingard - 7 Complimented Rashford to a tee. Excelled at getting in behind United's backline and provided a reliable outlet throughout. Manchester United 2 Chelsea 0 player ratings Asmir Begović - 6 Could have maybe done more for the first goal but unlucky about the second. Made some important saves to keep the score down. Manchester United 2 Chelsea 0 player ratings Kurt Zouma - 5 Stepped in to replace Marcos Alonso which subsequently disrupted the balance to Antonio Conte's team. Looked out of place. Manchester United 2 Chelsea 0 player ratings David Luiz - 5 Guilty of costly mistakes and, rather surprisingly, was overpowered at times by Rashford. A shadow of the player he has been this season. Manchester United 2 Chelsea 0 player ratings Gary Cahill - 4 Completely dropped his guard for United's second. Struggled to match Rashford for his pace and made multiple sloppy mistakes. An afternoon to forget for him. Manchester United 2 Chelsea 0 player ratings Victor Moses - 4 Anonymous and largely ineffective. Hauled off around the hour mark for Cesc Fabregas. Manchester United 2 Chelsea 0 player ratings N'Golo Kanté - 6 Showcased his ability to drive into space on a number of occasions but was overwhelmed physically throughout the match by Fellaini. Manchester United 2 Chelsea 0 player ratings Nemanja Matic - 5 Struggled defensively and seemed out of his depth. Couldn't deal with the United set-up. Manchester United 2 Chelsea 0 player ratings Cesar Azpilicueta - 6 Pushed forward down the flank and provided his team-mates with a reliable source of deliveries. Defensively, he enjoyed a better display than the rest of the Chelsea back line. Manchester United 2 Chelsea 0 player ratings Pedro - 5 Enjoyed a few half-chances but was subdued and lacked any real dynamism. Manchester United 2 Chelsea 0 player ratings Eden Hazard - 6 Missed that magic touch today. Was played out of the game by Herrera. Occasionally threatened with his quick feet but it wasn't to be. Manchester United 2 Chelsea 0 player ratings Diego Costa - 5 Bullish but another disappointing performance. His quality on the ball and in front of goal deteriorated as his composure faded throughout the game.

But that hasn’t stopped the 27-year-old fearing for his position at Old Trafford.

“I have to keep working, performing and giving what the manager wants me to give," Herrera told the club's website on Wednesday.

“We have great players and Manchester United has the capacity to sign big players, so I cannot sleep.”

Herrera has enjoyed a fine campaign (Getty)

United broke the world transfer record when they signed Paul Pogba from Juventus in August and manager Jose Mourinho is likely to continue revamping the squad when the transfer window opens in July.

Herrera has emerged as a key player under Mourinho, starting 23 of the United's 31 league fixtures so far this season compared with last season's 17 starts under Louis van Gaal.

Herrera marked Hazard out of the game (Getty)

"I am very thankful to him (Mourinho). This season has been the most regular one for me at the club and that is with Mourinho on the bench," he said.

"I am very happy. He gave me, from the first day, a lot of confidence and he told me I was going to be an important player for him."