Manager Kevin Keegan wants to keep Barton but Sportsmail has learned that several clubs have been made aware of the 25-year-old's availability.
Out of Toon: Joey Barton
Barton, who is serving a six-month prison sentence for assault and affray, is facing a further trial for allegedly assaulting former Manchester City team-mate Ousmane Dabo.
United chairman Chris Mort said: 'It is too early to say whether Joey being sacked is a possible outcome.'
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London gets ready for the Diamond Jubilee - in pictures
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EXCLUSIVE: I won't play with Joey Barton, says Adel Taarabt
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Diamond Jubilee: Boat by boat, here is where to watch the Queen's Thames flotilla - VIDEO
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Duchess of Cambridge is pretty in pink at her first Buckingham Palace garden party
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News pictures of the day
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Locked up and banned: The Tube drunk whose vile racist rant was caught on film (video)
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London 2012 Olympics: Raising the bar and the Games haven't even started yet. Price of toasting Team GB is £6 a pint! -
Timebomb ticking in Thames Estuary could put Boris Island plans in jeopardy -
Regent’s Park rapist: Teenage jogger assaulted by stranger in terrifying 7am attack -
Why I think doctors are right to strike 
Family pay tribute to the London man who gave his life to save a five-year-old girl from drowning 
Eton schoolboys fly Games flag on Everest 
Horror on the 5.53! Commuter dragged 200 feet after getting hand trapped on train 
Shrimpy's - review 
The O2
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Rock star
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Summer party
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Garden party
First review
Fair-weather goths
Dog save the Queen
