Middlesbrough boss Aitor Karanka believes Manchester City rival Pep Guardiola has underestimated the Premier League.

Karanka believes his compatriot has under-estimated the English league and says doubts still remain about his managerial ability.

"I think he needs to win the Premier League (to prove he is one of the best)," he said.

"This now is his toughest job, he has (previously) taken over at clubs who were already very strong. He has shown he can win titles in Spain with Barcelona and with Bayern Munich in Germany, and he probably thought he would do the same in England.

"But now I think he has realised that this is a different football, a different league, he has realised how difficult the challenge is.

"It's difficult when you arrive in a new country, with a new philosophy. He has some very good players, but the mentality here is different, the players are different and it takes time to adjust.

"When you have a squad like that, it is difficult to manage. It is taking him some time, it is not easy for him."