West Ham have agreed a deal in excess of £40m to sign Southampton midfielder Mateus Fernandes.
The 21-year-old has been granted permission to travel for a medical in London.
Fernandes would become West Ham's third-biggest signing, behind Sebastian Haller (£45m) and Lucas Paqueta (£51m).
The move will be a boost for under-pressure Hammers manager Graham Potter, whose side have lost their first three matches of the season in all competitions.
Southampton look set to make a substantial profit on the £15m they paid to sign Fernandes from Sporting last summer.
The Portugal Under-21 international has played 46 times for Saints, scoring four goals and providing seven assists.