Novak Djokovic complained to the umpire about the smell of cannabis during his Rogers Cup win over Jeremy Vardy in Canada.
The world No 1 said that the stench of someone "getting high" in the crowd was making him feel "dizzy".
"Someone is smoking weed, I can smell it, and I'm getting dizzy," he said to the umpire. "Somebody is getting high. Can you smell it? The whole place smells of it."
The Serbian ace told reporters after the match: "'I can't believe how bad it was."
Djokovic had said that had also noticed the smell during a doubles match with partner Janko Tipsarevic on Friday.
"Somebody is probably on the seventh sky somewhere. First in the doubles match, today again. Somebody's really enjoying his life around the tennis court."
It didn't affect his performance on the court, however, he beat the unseeded Frenchman Vardy 6-4, 6-2 in the semi-final.
The top seed will face Britain's Andy Murray in the final later on tonight. Murray beat Kei Nishikori in just 65 minutes to set up the Djokovic final.
The US Open gets underway on 31 August. Murray, the world No 3, has won the tournament once - back in 2012.
