Arsenal boss Arsene Wenger admits his former club captain is winning the title for Manchester United.
Wenger concedes Robin van Persie is firing Manchester United to the title.
The Arsenal boss said: "It is painful to see Manchester United so far in front of us."
The Gunners take on champs Manchester City tomorrow and could be an incredible 21 points behind leaders United - who signed Van Persie for £22million - by kick-off.
And Wenger added: "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."