LONDON—Discussing Viktor Troicki’s suspension for failing to take a blood test, Roger Federer says players must not be allowed to delay testing for any reason because of the potential for cheating.

“I don't know the conversation, the situation, exactly what happened,” Federer said of Troicki’s situation. "It's very important, I guess, the chaperone, the guy who comes and is next to you like a shadow, sometimes you don't know who that guy is. Sometimes they're a little hesitant because you just lost a match and you look extremely angry, so they don't dare to talk to you. They should probably just introduce themselves and say what is going on.

“Then you run to the toilet, [and you] can't go to the toilet. It's happened to me one time. Then the guy has to stay with you all night. It just becomes really complicated. But I do believe that when you are requested for a sample, you have to give the sample. It doesn't matter how bad you feel. I'm sorry. Like the test the next day for me is not a test anymore because what could have happened overnight. I don't believe anything. I believe whatever they decided on. I think it's just very important to give the sample when you're requested to give it because there you are in front of them and there is no way to escape anymore. That's where we just need to be extremely firm... Overall I trust the system.”

Troicki’s friend Novak Djokovic has said he no longer trusts the system, while Rafael Nadal says that while he believes Troicki did not take a performance-enhancing drug, the Serbian should have taken the test.

Andy Murray appeared to comment on the situation on Wednesday when he tweeted: “Read and respect the rules and everything is very simple.”