Ulf Karlsson served as coach of the Sweden track and field team from 2001 to 2004, guiding the country to a European Championship, a World Cup and Olympic gold. But a large section of the Swedish public has not taken kindly to Karlsson’s claims that Zlatan Ibrahimovic used performance-enhancing drugs while at Juventus aged 23.

“Zlatan put on 10 kilos in six months during his time at Juventus. I think he was doping, that’s how it seems to me,” Karlsson said in an interview with Sport Bladet.

Karlsson made his claim during a conference in Värmlands. When he was asked if he stood by his accusation, he responded. “Yes, I am convinced of it.”

Karlsson admits he used illegal substances on some of the athletes in his charge during his career and said that in team sports controls are less strict. Of Ibrahimovic’s weight gain at Juventus, he added: “He put on 10 kilos of muscle in six months. It’s impossible to do that in such a short space of time.”

Karlsson’s accusation was aimed at Juventus, as the doctor cited the example of another player at the club who he alleges used illegal substances. “[Hamburg and Sweden midfielder] Albin Ekdal put on eight kilos while he was at the club. I think there was a culture of it at Juventus. They had a club doctor who was suspended for 22 months.”

Ibrahimovic has never failed a doping control and could sue Karlsson over the allegations.