Barton has 18 months to run on his current contract.
Barton's agent, Willie McKay: "I believe West Ham made an enquiry for Joey and that was rejected by Newcastle.
"Joey is enjoying his football again and he is committed to Newcastle unless he is told otherwise.
"There are other sides interested in Joey as I have had five or six phone calls from teams asking about Joey's availability.
"If these interested clubs make an offer for Joey then it is up to the two clubs to agree a deal and once that happens then we can sit down and discuss a possible move."
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