Ander Herrera has warned the rest of the Premier League that Manchester United are close to hitting top form.

United secured impressive back-to-back away wins over Watford and Arsenal last week to stay in touch with Manchester City at the top of the table.

Herrera believes United are flying just at the right time as they welcome Pep Guardiola's side -- who hold an eight-point lead over their title rivals -- to Old Trafford on Sunday.

He told the club's official website: "We are going to find our best moment very soon. We are second and chasing to be top of the table.

"Jesse Lingard is on fire now, Paul Pogba as well, it's a pity he got a red card.

"Romelu Lukaku didn't score [against Arsenal] but he helped us a lot. The centre-backs -- Victor Lindelof is in fantastic form right now. So we are optimistic, of course."

Ander Herrera in action against Arsenal on Saturday. Julian Finney/Getty Images

Before the first Manchester derby of the season, United have a Champions League date with CSKA Moscow on Tuesday.

Jose Mourinho's team need a point to be sure of finishing top of Group A and Herrera insists they are not looking beyond that game.

He said: "I'm not thinking about Sunday, now it's about CSKA. We are not qualified yet so we don't think about City yet."

Meanwhile, United recorded their first win at the Emirates since 2014 on Saturday night and Mourinho's first away win against a top-six rival since he arrived at Old Trafford.

Two goals from Jesse Lingard and one from Antonio Valencia earned a 3-1 victory, although David De Gea was called on to make a record-equalling 14 saves.

"It was a fantastic result with some great performances," Herrera added.

"David was amazing, and we were clinical in the first half, with two chances in the first 15 minutes and two goals.

"Then of course Arsenal have a lot of quality and they were going to create chances, but for the two or three big ones they had, David was there so we're very happy."