The young striker, who previously played for Manchester United, has left the Hammers following the arrival of Javier Hernandez from Bayer Leverkusen
Middlesbrough have announced the signing of striker Ashley Fletcher from West Ham for £6.5 million.
West Ham are 14/1 to achieve a top-six finish
The 21-year-old signed a four-year contract after finalising terms with the Championship club on Thursday.
Fletcher follows Darren Randolph in leaving West Ham for Boro, the goalkeeper having completed a £5m switch last week.
— Middlesbrough FC (@Boro) July 28, 2017
He is Boro’s 11th signing in what has been a hectic transfer window for Garry Monk’s side.
The England youth international progressed through the Manchester United academy but signed a four-year deal with West Ham in July last year, having impressed during a six-month loan spell with Barnsley.
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He scored his only goal for the Hammers in a 4-1 EFL Cup defeat to his former club at Old Trafford in November.
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