Until Sunday Nibali had faced no more than three questions on the subject, but he is riding for the Astana team, whose manager Alexandre Vinokourov was banned for two years for blood doping in the 2007 Tour. Team Sky have a zero-tolerance policy for people with doping history.
The main reasons for Nibali's easy ride are that he has slowly worked his way up to cycling's pinnacle, and that his team are members of a key anti-doping initiative - the Movement for Credible Cycling (MPCC).
Froome's climb to the top of cycling was rather sudden, bursting into the limelight when he took second place in the 2011 Vuelta aged 26. Nibali's rise has been steady since he finished third in the time trial at the junior world championships aged 17.
Before taking the Tour's yellow jersey, Nibali had finished in the top 20 of his 11 grand tours, winning the 2010 Vuelta and last year's Giro.
It is therefore no surprise that he leads the Tour this year, having also always worked with the same coach, Italian Paolo Slongo.
MPCC has anti-doping rules stricter than those of the International Cycling Union: for instance a rider needing steroid-based drugs to heal an injury will be barred from racing for eight days.