Mystery still surrounded defending champion Rafael Nadal’s participation at Wimbledon after he lost a second warm-up match in two days but showed few obvious signs of pain from his knees on Friday.
The 23-year-old was beaten 4-6, 7-6, 10-3 by Switzerland's Stanislas Wawrinka in front of a couple of hundred spectators at an exclusive southwest London sports club before heading to Wimbledon where he was expected to talk about his fitness.
The match had been billed as a last-ditch test for the world number one who has been troubled by tendonitis in both knees since his shock early defeat at the French Open to Sweden's Robin Soderling.
During the match, the assembled media only had eyes for Nadal's knees. Nadal is scheduled to start his title defence against Frenchman Arnaud Clement.
Sixth seed Andy Roddick, twice a runner-up in London, could be lying in wait in the quarter-finals.
French Open champion Federer, in pursuit of a record 15th grand slam title, will open his account against Taiwan's Lu Yen-hsun.
However, he will have noted that he could run into Roland Garros runner-up Robin Soderling for the second time in less than a month in the last 16. Big-serving Croatian dangerman Ivo Karlovic lurks as a potential last-eight opponent.
British third seed Andy Murray, hoping to become the first home winner of the men's title since Fred Perry in 1936 and a potential semi-final opponent for Nadal, faces American Robert Kendrick in his opener.