Summerville, 24, was a rare bright spark for West Ham last season, scoring seven goals and providing three assists in his 34 games.
The Dutch winger has been heavily linked with a return to the Premier League following West Ham’s relegation, but Serie A side Roma had looked like his most likely destination.
Roma had made a bid worth €46 million for Summerville this month, while Man United had enquired about his situation and Aston Villa also expressed an interest.
Now, according to David Ornstein, Saudi Pro League side Al Hilal have blown Roma out of the water and agreed a massive €80 million deal.
A medical has now been scheduled, with Summerville expected to sign a long-term deal with the club.
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