Aitor Karanka is backing Alvaro Morata to be a Premier League hit with Chelsea, but feels Manchester United might have got the better deal with their big-money swoop for Romelu Lukaku.

Morata is set to become Chelsea's record signing on Thursday as he puts the finishing touches to a £70million switch to join Antonio Conte's men from Real Madrid.

The 24-year-old Spain striker came through the ranks at the Santiago Bernabeu when Karanka was on the coaching staff and the former Middlesbrough boss believes Chelsea have secured an elite operator perfectly suited to the challenge of the Premier League.

"He's a really good player, I've known him since he was 16 years old," Karanka told Sky Sports News.

"He's in the Spanish national team, Chelsea are signing a really good player with a lot of potential. He is a really good kid who is always looking to grow.

"I think he is perfect for the league because he is strong and powerful, he is good with the ball, good with the ball in the air and I think the most important thing for a young player is he wants to improve every single day. That's the main thing that means he can be successful there.

"The most important thing for a player is to know the coach knows you and the coach wants you. Antonio knows him very well so he has the confidence of the coach."

Conte sanctioned Juventus' move for Morata in 2014 – he enjoyed a successful two-year spell in Turin – but took over as Italy head coach before working with the player.

United manager Jose Mourinho has also worked with Lukaku before, who he sold to Everton during his second spell in charge of Chelsea.

Conte was reportedly furious when United beat Chelsea to Lukaku's signature, forcing a change of focus on to Morata, and Karanka feels the Belgium international's familiarity and prolific record in England's top flight could be crucial.

"I think maybe Man United has a little bit of an advantage because Lukaku knows the league and also knows Mourinho from when they were working together at Chelsea," he said.

"Alvaro also knows his coach but I think United have a little bit of an advantage."

Chelsea's search for a new striker was given added immediacy when Conte decided Diego Costa was no long part of his plans and Karanka was keen to point towards the temperamental differences between Morata and his combustible international colleague.

"I think they are different, especially in their character," he added. "Alvaro is completely different to Diego.

"Diego is a fighter, almost fighting. Alvaro is different. I don't want to say he is better with the ball but he can do different things.

"The main difference is their character. Alvaro is much calmer than Diego. He has a bright future in front of him.

"He can cope with the physical side. Italy is a strong league and at Real Madrid he scored important goals."