Arsenal manager Arsene Wenger has claimed that it is "painful" to see Manchester United do so well with Robin van Persie in their side.
The Dutchman left the Emirates Stadium for Old Trafford in the summer for £22m and his 16 league goals have helped the Red Devils move 18 points clear of the Gunners at the top of the table this season.
"It is painful to see Manchester United so far in front of us," Wenger told reporters. "You know when you sell Robin van Persie to United that will be the case.
"He is one of the best strikers in the world and you know he will score goals. He got 30 for us in the league last year."
Arsenal host champions Manchester City in the league on Sunday.
