Bollettieri (left) worked with Agassi for a decade
Nick Bollettieri believes Andre Agassi should be remembered for the good he has done rather than his drug use.
Agassi, who won the 1992 Wimbledon title under coach Bollettieri, admitted using crystal methamphetamine in 1997.
"I don't condone what he did - I've made mistakes too, but I've done more good than bad," he told BBC Sport.
"Let's look at what Andre has done, he funds a school for 400 kids from the inner-city. I know underneath he's a hell of guy."
Agassi, 39, who won eight Grand Slam titles, revealed in his new autobiography that he lied to tennis authorities about his use of the banned recreational substance, crystal methamphetamine.
The retired player had initially told governing body the Association of Tennis Professionals (ATP) that he took the drug accidentally.
That information was kept secret by the ATP.
If someone told him to include those thoughts in his book, then that's sad
Ex-coach Nick Bollettieri
Former Wimbledon champion Michael Stich suggested that Agassi was not suspended because he was important to tennis, but Bollettieri said that there should be no leeway when it comes to punishing drugs abusers.
"Whether you're number one or 1000 there can't be an exception," added the 78-year-old Bollettieri.
"If top players are found to be using drugs then they should be banned. That will send a message, stronger than any written message, 'we will not tolerate drugs'."
Agassi joined the renowned Bollettieri Tennis Academy, which has trained Maria Sharapova, the Williams sisters and Boris Becker among others, at the age of 13 before they parted company in 1993.
And Bollettieri said Agassi did not take drugs at his academy, as far as he knew.
"Our academy was rigid on the rules - we were probably as clean as any academy," he added.
"I'm sure along the way there would be have been somebody who managed to have a puff on marijuana. People can find a way to do that."
He added: "When Andre came to academy he was a free-spirit guy and that's what attracted me to him because I've always been a free-spirit guy.
"For a teenage Andre, image was everything. He changed his hair colour, wore rouge. He was rebellious, but also gifted.
"Andre did feel the time spent at the academy was beneficial, even though he also thought it was a concentration camp.
"But in a six-minute video speech at an anniversary event for me, he said he wouldn't have had the career he had if it wasn't for my help."
Bollettieri said he was also stunned by Agassi's admission that he hated tennis.
"He began playing the sport with his daddy in the garage with a ping-pong ball from the age of two - I never heard Andre said he hated tennis, never," added the American.
"If someone told him to include those thoughts in his book, then that's sad.
"But Andre is a big guy. Nobody had a gun to his head. Maybe Andre thought by bringing these things out, then it would help some people."