Roger Federer has no sympathy for Maria Sharapova, saying on Thursday he backs a "zero tolerance" stance against doping.

Russian star Sharapova was handed a two-year doping ban on Wednesday after testing positive for the banned medication meldonium at January's Australian Open.

The 29-year-old admitted in March she simply hadn't realized meldonium, which was added to the World Antio-Doping Agency's banned substance list in January, was no longer permitted.