World number three Stan Wawrinka has been forced to withdraw from the Rotterdam Open due to a knee injury.

Champion in 2015, Wawrinka had been penned in for a first appearance since his run to the Australian Open semi-finals as top seed in the Netherlands.

The Swiss had his right knee taped up during his epic five-set defeat to eventual champion Roger Federer in Melbourne and the issue is lingering.

Tournament Director Richard Krajicek said in a statement: "Stan called me [Tuesday] afternoon to share the bad news. 

"Test results showed that he is not able to play matches as a result of his knee. The medical advice came as a complete and unpleasant surprise. Not just for us, but for him as well."

Beaten Australian Open finalist Rafael Nadal is now top seed of the tournament, while Benoit Paire takes Wawrinka's spot.