Southampton manager Ralph Hasenhuttl has backed Timo Werner to be a huge hit at Chelsea.
The pair worked together at RB Leipzig and will face off this weekend in the Premier League.
"I have worked with a lot players and he is one of the quickest. He is really hard to defend against," the Austrian told reporters.
"He is getting a more complete striker now and is learning a lot. He is a fantastic signing for Chelsea and he is only happy when he scores, so I hope he is unhappy after the game. 'They haven't seen the best of him yet, at Chelsea, in his first games. He has only scored one goal, I think, in the [Carabao] cup.
"It would be a mistake to reduce Chelsea to just Timo, though. They have plenty of other good players in the squad.
"I hope I get to speak to him but not to congratulate him on a goal. I know this player very well. I had two fantastic years with him.
"We brought him in from Stuttgart for small money if you want. 'We knew the game that we played at Leipzig was perfect for him but he also showed development with the ball last year.
"He was fantastic for me in his first year and scored plenty of goals."
