Arsenal manager Arsene Wenger has questioned Chelsea's timing and motive in their sale of Juan Mata to Manchester United, the Guardian reports.

He fears that Chelsea's short-term aspirations have clouded the Blue's judgement in letting Mata move to a rival, albeit one that is struggling this season, and has warned Jose Mourinho he may later regret his decision.

Wenger believes the £40m was considered beneficial to Chelsea's push for the title as the Spaniard will be helping United in upcoming fixtures with Arsenal and Manchester City, who currently sitting first and second respectively.

After Chelsea's 3-1 victory over United last weekend, in which Mata was an unused substitute, Mourinho said with a smile that he now hopes the Red Devils "beat all of them [the top clubs] to finish fourth."

"He [Mourinho] sums up what Chelsea's thinking is," Wenger said, in regards to Mata.

He went on to stress that Chelsea aren't doing anything wrong but felt Mourinho was manipulating the market in an unfair manner.

"I am surprised because Juan Mata is a great player and they sell a great player to a direct opponent," Wenger said. "It opens [up] again a little bit the opportunity of this transfer market because Chelsea had already played twice against Man United so they don't play again. They could have sold him last week [before the United game].

"It opens, at least, the opportunity of the dates of this transfer window. Some teams have already played twice against one opponent and some others, not. If you want to respect the fairness for everybody exactly in the game, that should not happen. I just think you would want everybody on the same level. I can understand completely what Chelsea is doing. They do not do the rules but, maybe, the rules should be a bit more adapted to more fairness."

Wenger was however previously criticized for his sale of Robin Van Persie to Manchester United, who went on to win the title last season.

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