Momota, 21, in December became the first Japanese player to win the Badminton World Federation Super Series Masters Final and also gave Japan its first men's singles world championship medal by claiming bronze in Jakarta last August.
But Japanese badminton officials said on Thursday it would be hard to nominate Momota, who just recently rose to world number two, for a place at Rio after finding out that he and team mate Kenichi Tago had gambled at an illegal casino.
Tago, ranked 63 in the world, broke down in tears at a packed news conference on Friday at which he and Momota bowed deeply and apologised for betraying their nation's hopes.
"Even though I knew he was preparing for the Olympics, I didn't stop Momota from going," the 26-year-old Tago said, adding that even though he knew gambling was wrong he couldn't resist.
Most gambling is illegal in Japan and frequent gamblers could receive prison sentences.
Tears running down his face, Tago added: "I don't care what punishment I get, even if I can never play badminton again. My only wish is that you give Momota another chance."
A sombre Momota, dressed in a dark suit and black tie, said going to the Olympics had been a dream of his since childhood.
"I'm really sorry to those that have raised me to this day ..., " Momota said, occasionally biting his lip.
"I have betrayed all of them and I am deeply, terribly sorry."
Investigations by their domestic Nippon Telegraph and Telephone East Corp sides said that Tago had gone to several illegal casinos some 60 times in a two-year span, spending roughly 10 million yen ($91,800). Momota went six times.
Nippon Badminton Association secretary general Kinji Zeniya said on Thursday that it would "probably be impossible" for Momota to compete at the Aug. 5-21 Games in Rio. A final decision will be made this weekend, Japanese media said.
(Reporting by Elaine Lies. Editing by Patrick Johnston)
