Sports marketing pioneer Donald Dell is in stable condition in London's Royal Brompton Hospital after undergoing emergency surgery last week for a pulmonary embolism, according to U.S. Tennis Association chairman Alan Schwartz.

Dell, 66, a Washington native and founder of the city's Legg Mason Tennis Classic, was in England to attend Wimbledon when he became ill on Wednesday.

According to Schwartz, Dell initially had acid reflux diagnosed by a British physician. When the discomfort continued, he telephoned his physician in Washington and was urged to return to the hospital for a CAT scan in the lower part of his aorta.

Tests confirmed the embolism, and Dell was rushed to Royal Brompton Hospital in Chelsea, which specializes in cardio-thoracic care. He underwent 51/2 hours of surgery.

Dell was accompanied by his wife, and his daughters flew to London to be with him, Schwartz said.

"The news is very encouraging, and as of today he is a bit stronger," Schwartz said in a telephone interview Sunday.

Jo Thomas, head of communications at Royal Brompton Hospital, could only confirm that Dell was a patient there and in stable condition.

A standout tennis player at Yale, Dell served as captain of the 1968 and 1969 world champion U.S. Davis Cup team, which included Arthur Ashe and Stan Smith. Trained as a lawyer, his entry into sports marketing dovetailed with the advent of the Open era in professional tennis.

Dell went on to found ProServ, a leading sports marketing and management organization. He is chairman of ProServ and senior vice president of the SFX Sports Group.