MADRID – Olympic champion Rafa Nadal's withdrawal from the London Games because of injury deprived the tournament of one of its biggest attractions and left Spain reeling Thursday. The gold medal winner in Beijing four years ago has failed to recover from a knee problem, and also misses out on the honor of carrying his nation's flag at the opening ceremony. The Spanish tennis federation (RFET) said Feliciano Lopez would be his replacement in the singles while the country's Olympic committee (COE) said a meeting Friday would decide on a replacement flag bearer for the July 27th parade. “I'm not in a condition to be able to compete," Nadal, 26, said in a statement. “Today is one of the saddest days of my career as it was one of my biggest dreams, and perhaps the most anticipated moment to be the flag bearer at the opening ceremony for the Games in London. You can imagine how difficult it has been to take this decision." Meanwhile, strikes by train drivers and passport officials threaten major disruptions to the London Olympics, prompting the government to warn unions Thursday that they risked public anger if the industrial action went ahead. The Aslef rail union announced Thursday that 450 of its members in central England would walk out between Aug. 6 and 8 in a dispute over pensions, affecting passengers travelling from cities such as Sheffield, Nottingham and Derby to the capital. The decision coincided with a move by border officials to strike on July 26, the day before the start of the Games, potentially delaying thousands of visitors arriving for the showpiece event. The threat of transport chaos added to pressure on the government, which has already had to call in thousands of extra soldiers to guard the Games after a failed private sector recruitment drive left an embarrassing hole in security. The July 27 evening ceremonyhas already been shortened to avoid a possible late-night rush for trains and buses home. — Agencies