Spanish world number two Rafael Nadal has pulled out of the opening rubber of his country's Davis Cup World Group first round tie with Switzerland, after straining a muscle in training.

Nadal's withdrawal was announced by tournament officials just half an hour before he was due to face Swiss number three Marco Chiudinelli in Friday's first singles match.

Nadal's place will be taken by world number 33 Fernando Verdasco, who was originally due to contest only Saturday's doubles rubber alongside Feliciano Lopez.

It was not clear whether Nadal would be fit enough to play in Sunday's reverse singles.

Switzerland were hit by a similar blow on Thursday when their top-seeded player Stanislas Wawrinka was forced to withdraw after tearing a knee ligament in training.

The Swiss were already having to do without world number one Roger Federer, who decided to skip the opening round to concentrate on his own career.

Wawrinka, who was due to play Friday's second singles rubber against Spanish world number 15 David Ferrer, has been replaced by Stephane Bohli -- a Davis Cup debutant who has never won a match on the ATP circuit.