Haas is currently the world number 17
Germany's Tommy Haas has pulled out of this week's Davidoff Swiss Indoors tennis tournament in Basle after contracting swine flu.
The 31-year-old consulted his doctor after suffering flu symptoms and was diagnosed with the H1N1 strain.
"I did a test because I suspected I had the swine flu and it was positive," this year's Wimbledon semi-finalist told the Bild newspaper.
Haas also withdrew from the Stockholm Open in October because of flu.
He added: "I am quite relaxed because I know that swine flu is a particularly strong form of flu but when you are in a good physical condition like I am, then you can quickly beat it off.
"It was really bad for three days and I couldn't leave my hotel room. I felt really bad."