The 19-year-old has refused a month's extension to his contract and can leave the club on June 30 with Watford and Bundesliga side Schalke understood to be among those interested in signing him, says the Daily Mail.
Ngakia figured in the final 30 minute segment of Saturday's friendly against Crystal Palace and scored in the 2-1 win.
Hammers boss David Moyes is understood to be frustrated as he believes the issue is not based on finance while he has also proved he is willing to give the youngster a run in his first team as long as his performances merit it.
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