Chris Froome claims he had urine thrown towards him by a fan during stage 14 of the Tour de France.
The man allegedly shouted 'doper' at the Team Sky rider during the incident around 30 miles into the stage from Rodez to Mende.
Froome shrugged off the act by increasing his lead in the battle for the overall classification, but admitted it left a sour note.
The 2013 winner insisted the unfounded doping slurs he is being faced with would not affect him but pleaded for fans not to interfere with the race result.
The Kenya-born rider, 30, said: "I saw the guy. It was on a drag about 50, 60kms into the race.
"I had some team-mates around me, they also saw the incident. I was boxed in a little bit on the left, so I couldn't move away from it.
"I saw this guy just peering around - it looked a bit strange - and as I got there he just launched this cup towards me and said 'doper'. There's no mistake it was urine.
"That's unacceptable on so many different levels."
The incident came just days after teammate Richie Porte was punched in the ribs. Sky have also stepped up security around their team bus after cars were pelted with coke cans during the stage.
Froome believes he has been singled out by a few individuals for accusations given his form in the mountain stages.
The Monaco-based rider knows there is little protection on the roads, especially when they hit the Alps next week as fans line the tight route.
It would be easy for one individual to try and push him off his bike which could wreck his hopes of regaining the title.
But Froome added: "I'm not scared about this. I just hope it doesn't interfere with the racing.
"That's why we're all here. We're all here to race our bikes. I'm staying extremely focused on my job that I'm here to do. I'm not going to let anything put me off.
"I certainly wouldn't blame the public for this. It really is the minority of people out there who are ruining it for everyone else. I would blame some of the reporting on the race, that has been very irresponsible.
"Those individuals know who they are. It is not all the media."
Froome leads by three minutes and 10 seconds from Nairo Quintana after the Colombian moved into second place in a stage won by Britain's Steve Cummings.