Alexander Povetkin, the Russian, who will face him at the Wembley Stadium on September 22, for the world heavyweight titles, tested positive for steroids twice in 2016 and was suspended indefinitely by the WBC. He was also imposed a $250,000 fine.
The ban has since been lifted and Povetkin came to London on Wednesday to pose for pictures on the Wembley turf with Joshua.
“If I missed a test or was even an hour late for one people would say oh, he must be doping.
“They would deal with me (if I failed a test) and I know they would make an example of me and I would never be able to box again.
“It will never happen because I would rather take a loss than be caught doping, which is far worse for your legacy. If you lose you can respect the man who beats you and bounce back.
“Drugs don’t make you a better fighter. I prefer to work hard and stay clean and do the best I can in every fight,” Joshua said.
Povetkin lost big money when world title fights against Deontay Wilder and Bermaine Stiverne were called off, after he failed drugs tests.