Boris Becker has stood by his criticism of Andy Murray by stating that tennis is a clean sport and "rumours are not reality".
World number two Murray said in an interview with the Mail on Sunday that he had been suspicious that opponents may have been guilty of doping as they did not appear to be getting tired.
Becker was not impressed with the two-time grand slam winner's comments, which the legendary German insists are wide of the mark.
The 48-year-old, who won six grand slam titles in his illustrious career and now coach's world number one Novak Djokovic, said Murray should be more careful with his comments in future.
Speaking at the Laureus World Sport Awards, Becker said: "Andy is a friend, I like Andy and respect him and I think he's done amazing things and will do amazing things in the next couple of years, but I have to put my friendship aside and protect the sport a little bit.
"Rumours are not reality. Tennis is an Olympic sport. All the top guys, I know for a fact, get tested a lot. Everybody is clean and so we can't spread rumours.
"If Murray feels that he lost a match because the other guy was running longer than him it's because of the fitness, otherwise we would have known.
"He [Murray] is one of the fittest players on the tour, he is very dedicated, puts a lot of effort into his training and so are the others."
Becker added: "There's been rumours about Rafa [Nadal] over the years, there have been to a lesser extent about Novak. I find that incredibly disrespectful to both players. They are legends, they are super athletes, they live and breathe tennis.
"I would find it equally disrespectful to Andy if somebody claimed he only won Wimbledon because he took a pill. I think that's wrong and that shouldn't be allowed.
"So that was my comment and I stand with it because it's about the integrity of tennis. I felt that I needed to defend it a little bit.
"I don't know what stories he's heard. In the locker room people talk a lot, the days are long. A lot of players lose early, so they show their frustration with talking maybe a bit too much.
"What is talked about and the rumours is one thing and reality is the other thing. If you are such an important player as Andy he has to work media on his feet a lot on a weekly basis, you just have to be careful about what message you bring across.
"I have been around before Novak, I love my sport, I defend my sport and that's where I'm coming from. I'm not speaking on Novak's behalf."