Four-time world champion Daiya Seto has been suspended for the rest of the year for breaching the Japan Swimming Federation's sportsmanlike conduct standards due to a scandal over an extramarital affair.
The federation handed down the punishment following an extraordinary meeting late on Tuesday but Seto will be eligible for next year's Tokyo Olympics.
Seto, the reigning world champion in the men's 200 metres and 400m individual medley, resigned as captain of Japan's Olympic swim team last month after admitting to the affair.
"How can I apologise? I have been asking myself if I can, but I think my apology is to continue swimming, restoring the trust of my family, who have been deeply hurt by my irresponsible behaviour," sports daily Hochi Sports quoted him as saying.
"I would like to seriously face swimming with the determination to start over so that my family and everyone will recognise me as a swimmer again. I'm really sorry."
The scandal has tarnished Seto's reputation and he has already agreed to sever ties with sponsor All Nippon Airways.
Seto won a bronze medal at the Rio Olympics in 2016.