WASHINGTON - Richard Holbrooke, the US special envoy for Pakistan and Afghanistan, underwent another surgery Sunday after a 20-hour operation that ended Saturday, the State Department said. Sundays seven-hour procedure was necessary after surgery to repair a tear in his aorta was slowed by the failure of his blood to clot, according to a media report, citing family friends. Holbrookes family is grateful for the outpouring of support and prayers coming in from his many friends, colleagues and leaders around the world, State Department spokesman Philip J. Crowley said in an e-mailed statement. Among the telephone callers to Holbrookes wife, Kati Morton, was President Asif Ali Zardari. Holbrooke isnt out of danger and prospects for recovery may not be clear for several days, the family friends said. He was admitted to George Washington University Hospital on Dec 10 suffering from an aortic bleed, White House adviser David Axelrod told CNN. Reuters adds: Richard Holbrooke is stable but in very critical condition, US Secretary of State Hillary Clinton said on Monday. He is stable but still in very critical condition, Clinton told reporters at a news conference with the Canadian and Mexican foreign ministers.