The Hammers were hoping to lure the 19-year old Frenchman to Upton Park on a loan deal this summer but his agent has confirmed that the player has turned down the overtures from east London.
"On Monday I met with West Ham, who were interested in the player," Niang's agent Stephane Courbis told TMW.
"The Hammers would like him on loan, but I don't think it is the right choice, so I excluded it.
"We prefer a permanent deal and we seek a coach who strongly believes in Niang."
Niang, who spent the second half of last season on loan with Montpellier, is looking for a permanent move away from Milan according to Courbis.
"Milan, he told me, have many forwards in the group and, with not playing in Europe, there will be reduced places," he added.
"For this reason, we were told to find another team. M'baye could leave on a permanent move."
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