Arsenal boss Arsene Wenger has voiced surprise that Chelsea could sell playmaker Juan Mata to Manchester United.Mata is expected to undergo a medical at United ahead of a potential club record move to Old Trafford.
A source close to negotiations has told Press Association Sport that a deal is "close" to being completed and Mata could be in the United squad to face Cardiff next Tuesday.
Mata, 25, has fallen out of favour at Chelsea this season but Wenger is still amazed he could be allowed to join a traditional title rival.
Asked if he was surprised, Wenger said: "Yes I am because Juan Mata is a great player and they sell a great player to a direct opponent."
Wenger does note, however, the timing of the move with Mata now unable to affect Chelsea directly this season as they have already played United twice in the Barclays Premier League.
Chelsea beat the champions 3-1 at Stamford Bridge last weekend, a result that left United seventh in the table.
Chelsea could still come up against United in the Champions League but Mata would be ineligible.
With the Premier League fixture list in mind, Wenger is not sure the January transfer window is a fair concept.
The Gunners boss said: "Chelsea had already played twice against Man United so they don't play again any more.
"They could have sold him last week but it opens up again questions about the dates of this transfer window.
"Some teams have already played twice against one opponent and some others not.
"I think if you want to respect the fairness for everybody exactly the same, that should not happen."
But Wenger said: "I wouldn't go as far as that. I just think you would want everybody on the same level.
"I can understand completely what Chelsea are doing. They do not make the rules, but maybe the rules should be a bit more adapted for more fairness."