As the riders got into Wettingem at the end of a 192km fourth stage from Schwarzenburg, there was a bunch sprint in which the HTC Colombia rider made a surge for the line.
Cavendish went for the line but there was a coming together with Haussler. Both riders hit the deck, with others coming over the top of the Manxman including Tom Boonen.
Around ten riders went down as Lampre rider Alessandro Petacchi avoided the crash to win the stage.
Mark Cavendish
Cavendish was seen by his team's doctor and was initially diagnosed with severe road rash and mjor bruising. He is to under go further tests.
HTC Colombia rider Tony Martin remains the leader of the General Classification. Martin remains determined to keep his lead ahead of local hero Fabian Cancellera and told his team's Press Office: "My initial idea was to come to Suisse mainly as part of my build-up for the Tour de France. But this is a very prestigious race, I'm very proud to be in the lead, and I've no intention of letting it go easily.
"The next two stages are more for the sprinters, it's stage six on Thursday which will be the big test."
Picture copyright of Covsupport News Service. Credit CNS/KM