Ashley Fletcher will hold talks with Middlesbrough after they agreed a fee with West Ham.
The 21-year-old striker has left the Hammers' training camp in Germany ahead of the proposed move, Boro have confirmed.
Reports have suggested the fee is around £7million as Boro continue to spend big as they seek an immediate return to the Premier League.
A club statement read: "Boro have agreed a deal in principle with West Ham United to sign striker Ashley Fletcher.
"The former Manchester United youth player has left West Ham's training camp in Germany and is heading to Boro for talks.