Rossi admits his time in England taught him a lot - and paid tribute to the influence of Sir Alex Ferguson for nurturing his career, despite the hitman failing to make the grade at Old Trafford.
The 21-year-old told the Sunday Mail: "I grew a lot as a player and person at United. When you're at one of the best clubs in the world it can only help your development.
"Sir Alex was always good to me. He helped me a lot and gave me plenty of advice so I can't thank him enough.
"I'm not disappointed I didn't make it at United. There were three or four world-class strikers ahead of me and it's hard for a youngster to get a chance.
"The best option was to leave and try a new experience. I did that firstly by going to Newcastle on loan then joining Villarreal. I've remained at a high level in La Liga and Spain has been enjoyable so far, the football and the lifestyle.
"We have a strong squad with great players and last season was wonderful with us finishing second in La Liga.
"To be successful you need a strong team spirit and we're a bunch of friends as well as a squad of players."