LONDON - World number one Rafa Nadal faces one of the biggest matches of his career on Friday in front of a few hundred spectators at an exclusive southwest London sports club.

The 23-year-old will play Switzerland's Stanislas Wawrinka in an exhibition match which may not only decide whether he defends the Wimbledon crown he won so gloriously last year but also if his painful knees can permanently derail his glittered career.

The Mallorcan winced and grimaced his way through a two-set defeat against Lleyton Hewitt at the aristocratic Hurlingham Club on Thursday.

Lesser men who did not have the world's biggest grasscourt title to defend would have already given up the ghost and returned home to recover properly.

But Nadal is nothing if not a fighter and with his Roland Garros crown gone he will pull out all the stops to take his place in the 128-man field for the year's third grand slam starting on Monday, when the men's champion is traditionally scheduled to open his defence.

"Rafa is having difficulties bending his knees and it (seems) that his various treatments are not enough," his coach and uncle Toni Nadal told reporters after the defeat by Hewitt, whom Nadal walloped for the loss of just five games in Paris last month.

"It was a real test," British media reported Nadal as saying after the match.

"I will come back tomorrow and play and then make my decision about playing Wimbledon or not."

Nadal was stunned by Robin Soderling in the fourth round of the French Open and he then withdrew from the Queen's Club tournament, shunning the chance to defend another title in favour of nursing his aching joints for Wimbledon.

Few who watched his laboured movements on Thursday could believe he will be up to the rigours of a seven-match defence of his Wimbledon title over the next fortnight, and fans will fear his presence in the draw to be made this lunchtime will be shortlived.

--REUTERS