Andre Agassi was shocked and saddened by disgraced cyclist Lance Armstrong's confession to using performance-enhancing drugs and the eight-times grand slam champion said tighter, more frequent dope testing procedures in tennis would be good for the sport, Reuters said.

The American, who co-founded a philanthropic organisation with Armstrong and other athletes like Muhammad Ali, women's World Cup winner Mia Hamm and NBA champion Alonzo Mourning, said he had been convinced of Armstrong's innocence.

"Well, my reaction to it is the same as everybody. It was shock, hard to stomach, sadness, disappointment. I think 'anger' is a fair word," Agassi told reporters at Melbourne Park on Friday, January 25.

"I was certainly one of those that flat out believed him that long period of time. The thought of it not being the case was unconscionable to me."

Armstrong, 41, admitted in an interview with Oprah Winfrey last week that he used performance-enhancing drugs and lied about it for over decade, finally owning up to being at the centre of one of the biggest drug scandals in world sport.