Carvalho, 32, said: "When I went to Chelsea it was much more difficult for me than moving to Madrid. I grew up in Portugal and football there is very similar to the football here in Spain. I think its a lot harder to play in the Premier League.
"Players are physically much stronger in England. In that sense it's harder to play for Chelsea than for Madrid. And playing there is what has really improved me as a player. I had six very happy years at Chelsea."