New Zealand cyclist Greg Henderson is facing legal action after accusing Fabio Aru of feigning illness to cover up issues with his biological passport.
The Italian rider missed the Giro del Trentino with a stomach ailment, which prompted Henderson, who rides for the Belgian Lotto-Soudal road racing team, to question his sickness and label him a cheat.
"Sad to see @fabaro1 'sick'. Mate make sure next time u come back to our sport 'healthy'. Aka Clean! #biopassport! Or don't come back!" Henderson wrote on Twitter.
Henderson, who won gold for New Zealand on the track at the 2002 Commonwealth Games, followed it up with another tweet. "I am so sick of it. It becomes common knowledge within days. Why try cheat."
He quickly removed the Twitter posts, before issuing an apology the next morning.
"When you are sick. You are sick. Jumping to conclusions helps nobody. My mistake @FabioAru1. I should shut my mouth. Sincere apologies."
A statement on Aru's website says he's empowered his attorney to take legal action against the New Zealander in order to defend his image and respectability.
Aru's agent Alex Carera joined the debate over the weekend.
"A famous athlete like Greg Henderson who has 30,000 followers on Twitter can cause huge damage to a person like Fabio, his Astana team, and the sport," said Carera. "Our lawyers will look at what has happened and consider where to start legal action."
The International Cycling Union recently investigated Astana in relation to anti-doping issues. The outcome of the review was that Astana would retain its top-tier racing status but would be "subject to strict monitoring".