Italian swimmers Filippo Magnini and Michele Santucci will be probed by the country's anti-doping organisation, according to reports.
The duo will be quizzed by the Italian National Doping Organisation for "use or attempted use of doping products", AFP reported.
It is connected to an investigation into nutritionist and doctor Guido Porcellini, with Magnini, a four-time world champion, already playing down the speculation.
La Gazzetta dello Sport reported allegations that doping products acquired by Porcellini were destined for Magnini, but that he never received or used them.
The newspaper also reported that a previous investigation into Magnini was ended due to a lack of evidence.
ANSA reported that the case surrounded the suspected traffic of anabolic steroids and other banned substances from China.
Magnini responded to the reports on Twitter, saying: "I believe that the probe is an obligation linked to the criminal investigation into Porcellini.
"Investigators have already established that I had nothing to do with this case.
"Let's be clear, thanks."
Porcellini is due to appear in court in Pesaro on November 7.
Thirty-five-year-old Magnini won the 100 metres freestyle titles at the long-course World Championships in 2005 and 2007, with the latter victory shared alongside Brent Hayden of Canada.
He also boasts two short course relay world titles and an Olympic bronze in the 4x200m freestyle relay from Athens 2004, as well as 17 European gold medals across long-course and short-course events.
Twenty-eight-year-old Santucci won long-course World Championship bronze in the 4x100m relay in 2015.
In 2006 he won two junior world titles in relays.