Rafael Nadal will play one last semi-serious match this afternoon before deciding if he should risk his fragile knees and walk out on Monday to defend his Wimbledon singles title.

The Spaniard’s crestfallen manner for much of the 72 hours he has spent in London suggests that even if he chooses to play, he surely cannot last a full two weeks.

Nadal has confirmed that he will make up his mind after a match against Stanislas Wawrinka, of Switzerland, as part of the BNP Paribas Fortis Challenge at the Hurlingham Club, West London. At the same venue yesterday, he looked discomfited and anxious in a straight-sets loss to Lleyton Hewitt, the 2002 Wimbledon champion.

“Today was as close to reality as I could get,” said Nadal, whose defeat in the fourth round of the French Open to Robin Söderling, of Sweden, was the shock of the year. “It was a real test. I will come back tomorrow and play and then make my decision about playing Wimbledon or not.”

After his premature exit in Paris and a few days of rest at home in Majorca, Nadal flew to Barcelona for tests that confirmed tendinitis in both kneecaps.

“More speed — bigger problems,” Nadal’s doctor, Ángel Ruiz-Cotorro, said this week. “Tennis has changed a great deal. We used to talk about injuries: the elbow, the shoulder, the wrist. But in recent years, with the change in equipment materials — the rackets, mostly, but also the strings — we have new pathologies. Everything’s faster. You’re hitting the ball faster and harder, and in new positions, which creates problems with the spine, the knees, even the hips.”

Such a diagnosis is worrying enough for every player in the long term. For Nadal, 23, he has to hope that he can play without any lingering pain. “Rafa is having difficulties bending his knees and it seems that his various treatments are not enough,” Toni Nadal, his coach and uncle, said after the defeat to Hewitt.

When Toni urged his nephew to “bend down” to the ball during the second set yesterday, the Wimbledon champion appeared to mutter, “I can’t.”

The loss of Nadal, who won the title in dramatic style against Roger Federer last July, would rob the Championships of a lot of their sheen and would lead to a revision of the draw, which is made this morning. Should any of the top four seeds drop out before Monday’s order of play is issued, the No 5 seed — in this case Juan Martín del Potro, of Argentina — moves into the vacant slot, with his place taken by the No 17 seed, David Ferrer, from Spain. The 33rd player on the men’s list would then slide into Ferrer’s position and a lucky loser from qualifying would fill the final slot.

There will be a shuffling of the seeded pack, too, with the news that Gaël Monfils, the French No 14 seed has withdrawn from Wimbledon with the wrist injury suffered in a fall in the AEGON Championships at the Queen’s Club last week. Monfils, like Nadal, is one of the characters of the men’s game and his absence is a blow. On the plus side, Taylor Dent, the American who almost left tennis after a series of back problems, won his first best-of-five-set match since his comeback to the tour this year to qualify.

The final hope of a British qualifier making it through the competition this year was dashed when Naomi Cavaday, of Kent, lost 7-5, 6-2 to Vesna Manasieva, of Russia. Karen Cross remains the last British woman to have successfully qualified for Wimbledon, eight years ago.