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The Toffees full-back has enjoyed an excellent season at Goodison Park, appearing in the Professional Footballers' Association Team of the Year and receiving international recognition with a call-up for England’s Euro 2012 squad.
With current United left-back Patrice Evra set to turn 32 next month, reports are suggesting Sir Alex is on the hunt for a replacement for the French international and that Baines is the Scot's number one target.
United chief executive David Gill is reported to have already contacted Everton chairman Bill Kenwright over the possibility of signing the England left-back.
The Red Devils are said to be willing to fork out £12m for the 27-year-old, though Kenwright is unlikely to accept anything lower than Everton’s £15m valuation of the player.
Although Everton are said to be reluctant to part with the highly-rated defender, David Moyes has been known to deploy Sylvain Distin at left-back in Baines’ absence, meaning the club would not necessarily have to sign a replacement and may be more willing to sell for the right fee.