Simone Zaza has claimed that his time at West Ham United was unsuccessful because he "was not right mentally".
The 25-year-old joined the Premier League side on loan from Juventus in the summer but failed to score for them in 11 appearances.
Zaza is quoted by Sky Sports News as saying: "It was a very difficult time for me. When I joined from Juventus I was very optimistic, I wanted to experience playing in England because I thought it was the football that I liked and where I could use my qualities.
"Everything started badly from the outset, I think the main blame lies with me because I was not right mentally, I was very negative and in all the things that happened I never saw the positive side.
"There was an atmosphere, a culture very different to mine. That was a problem. Now I'm here [in Spain] I feel bad not to have shown in England what I'm capable of."
Zaza has moved to the Mestalla on an initial six-month deal.