Fornals says he couldn't see himself playing for another club in England.
He told the Athletic: "I had interest from another Premier League team, but there was no way I could join another club in England. It would be strange to play against the club I love.
"It's easier to live in London than in other European countries, but if it's not West Ham there's no chance. Even if it was Manchester City or Manchester United ... I can't do it. I can't imagine myself scoring or celebrating a goal against West Ham.
"I joined a year before the pandemic started and spent a lot of time without my family. When I needed that bit of affection in difficult times, the club was always there for me. I am very grateful to have been at West Ham during one of the most successful times in the club's history. We qualified for Europe three years in a row , we won a trophy and even the fans have a chant for me."