Roger Federer wants tennis to get tougher on its anti-doping programme, but Novak Djokovic believes some of the rules are already too strict.
The multi-Grand Slam winning duo been having their say ahead of athletics officials deciding on whether to suspend Russia over widespread doping.
Federer wants to see more testing, particularly at the latter stages of tournaments, commenting: "We have a very clear thing of what we should be doing - more testing."
Djokovic thinks the demands for players to tell doping officers where they are all the time can be "a bit too much".
"The whereabouts demands are a little bit too much and a bit unnecessary to write where you are every single day of the year," he said.
"If you don't appear at the place where it is written down then you get a warning, then two warnings and then suspension. I think that is a bit too much. The tennis season is very long. They know where we are and they can find us. When you're in the off-season you are going back and forth and changing cities and locations and it can be hard to track down and fill in the whereabouts sheet."
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