RAFAEL NADAL expects to miss up to four weeks with the knee injury that forced him to retire during his Australian Open quarterfinal against Andy Murray.

The world number two had his right knee assessed in Spain on Thursday and was advised to rest completely for two weeks before another fortnight of training and medical treatment.

The news means Nadal is set to miss the ABN AMRO World Tournament in Rotterdam next month, where he reached the final last year before losing to Murray.

However, the injury is not a recurrence of the tendinitis that has proved increasingly troublesome for Nadal and caused him to miss the defence of his Wimbledon title last year.

Laura Robson, meanwhile, reached the final of the Australian Open girls’ championships with a straight-sets win over Kristyna Pliskova of the Czech Republic.

The Briton cruised to a 6-3 6-1 triumph in 65 minutes.

Robson converted five of her 13 break opportunities, dropping her own serve just once.

■ Venus and Serena Williams beat Cara Black and Liezel Huber to win the women’s doubles title at the Australian Open. The sisters, the number two seeds, won 64- 6-3 to take the title for the fourth time.

Serena Williams takes on returning Belgian Justine Henin in the women’s singles final today.