Paralympic swimming champions Dave Roberts and Sascha Kindred have both been forced to pull out of next month's European Championships in Berlin.
Roberts has failed to recover in time from the broken elbow he suffered earlier this year.
Kindred, who is hoping to appear in his fifth Paralympic Games in London, has a back problem.
The championships run from 3-10 July and are the last major international event before London 2012.
Kindred will miss out on defending the 100m breaststroke title he has held since 1995.
"I am obviously really disappointed not to be able to attend the Europeans but I feel that with my ongoing back problem, competing at such a high level would have been detrimental for my recovery and my focus now will be on London 2012," he said.
Welshman Roberts is Britain's most successful Paralympian of the modern era, alongside compatriot wheelchair racer Baroness Tanni Grey-Thompson, with 11 gold medals.
But since the Beijing Paralympics, where he won gold in the 50m freestyle, 100m freestyle, 400m freestyle and 4x100m freestyle, he has had a number of injury worries including rib and shoulder problems, as well as kidney stones.
He said: "I am massively disappointed to be missing the European Championships. It was the final chance to test myself against the best in the world in Germany before the London Paralympics.
"Everything now points towards preparing meticulously with my coach for 2012. It's a once-in-a-lifetime opportunity to compete at a home Games and for me, winning a 12th Paralympic gold would be a dream come true."