Severin Luthi has played a key role in the Roger Federer's career. The Swiss player hired Luthi back in 2008, and since then he often praised the work they have done together. At the end of 2015, when Stefan Edberg decided to leave the team, Federer asked Luthi to become his main and one coach.
The 41-year-old didn't accept the request as he works as Swiss Davis Cup team captain and cannot guarantee a 365-day (or so) availability a year. Speaking at the ATP Finals in London last year about Luthi, Federer said: 'I do believe he doesn't get the credit he deserves because he doesn't speak to you guys or the press very often.
He didn't want to do it for years. He doesn't want to polish up his reputation. He's there trying to help me as much as possible. He's a great friend, especially a great coach for me, otherwise, he wouldn't be on the team.
If he was just a friend, I think he would do work. As a coach, he's really valuable to me. He knows my game very well. He knows my practice sessions very well. He knows what I need to work on. He knows what makes me happy and sad.
He knows my team members very well. So he's crucial to the team. But I do believe that he doesn't get the credit he deserves, yes.'