Andy Murray has admitted that he thinks more can be done in the fight against drugs in sport.
The US Open champion believes that the element of surprise remains remains a strong weapon for drug testers and has called for more to done by the International Tennis Federation.
He told The Telegraph: "You never know in any sport what's really going on.
"I think the out-of-competition stuff could probably get better. When we're in December and stuff, when people are training and setting their bases, I think it would be good to try and do more around that time.
"On Saturday night, we actually had a blood test. They came to the hotel late that night, it was completely random. I think that's good, we're not used to doing that many blood tests in tennis and it's something that's obviously necessary."
Murray begins his Paris Masters campaign on Wednesday with a second-round match against either Paul-Henri Mathieu or Roberto Bautista-Agut.