He was referring to Sampras having thalassimia minor....Sampras kept it quiet as not to further allow his opponents to gain an edge on him.
What about him fighting his way through a swollen foot that required cortisone injections to earn his seventh Wimbledon title and thirteenth grand slam title? It was reported that he didn't practice and had a hard time walking and only hit the courts for his matches during the whole second week of the fortnight. He got injections prior to the match, but they wore off due to the rain delay. The doctor refused to inject it again and he went out, played, and won.
"The secret is to find your motivation every single time - your inner motivation - so I always want to improve myself..." - EV