Arsenal boss Arsene Wenger has said that Juan Mata's proposed move from Chelsea to Manchester United raises questions about the fairness of the January transfer window.
Chelsea is two points behind Premier League leaders Arsenal and has played United twice this season.
Wenger said maybe the rules should be adapted for more fairness, as it opens up questions about the dates of this transfer window.
Last year, Wenger asked the clubs to limit their signing to only two new players in the January window.