The British newspaper claim that Italian club Sampdoria are interested in the Ecuador international forward.
Valencia joined West Ham from Pachuca in the summer of 2014 and had a successful debut Premier League season.
The former Emelec star scored four goals and created 17 chances in 32 league matches, and had a pass accuracy of 77% and a shot accuracy of 47%.
Although the 25-year-old is a very good player, it is unlikely that Sampdoria or any other club will pay £30m.
After all, Valencia has had one good season in a top league; there is no guarantee that he will be able to repeat his performances of the 2014-15 campaign next season.
Chelsea are also interested in the Ecuadorian, as reported by The Mirror, but even the Premier League champions would not be willing to part with £30m for a player who is not world class.