In contrast, fellow Irishman and notorious hot-head Conor McGregor would sooner pick daisies with Nate Diaz than bet against himself on a match.
Fellow boxer Michael Conlan was in the same boat as Donnelly, placing a bet "just for fun" while struggling to find things to do in the Olympic village.
Granted, this Irishman didn't bet against himself - but the IOC still had a bone to pick with the two.
The unlucky punters were reprimanded for breaching their Olympic contract which prohibits gambling on events to prevent instances of match-fixing.
"Participants at the Olympic Games are not permitted to bet on Olympic events and are obliged to report any approach or suspicion of manipulation," a statement said.
Donnelly faced the Olympic Committee Disciplinary Commission and said he'd "bet without intending to cheat by losing his match to win his bets, rather, winning the bets would be some compensation in the event he lost his match".
Donnelly posted this hilarious reaction to Twitter after his embarrassing gambling gaffe was revealed.
Donnelly missed his shot at a medal after being defeated by Morocco's Mohammed Rabii in the quarter-finals, while Conlan experienced a bumpy Rio campaign marred by controversy in the ring.
The 24-year-old lost to Russia's Vladimir Nikitin in a divisive decision which caused a backlash against corruption in amateur boxing.
Despite making a mess of Nikitin's face - an injury which eventually led him to retire from Rio - Conlan was declared the loser by unanimous decision.
The bantamweight battler fired back instantly, calling out everyone from the referee to the judges.
"I was in first gear and I was boxing the ears off him. I don't know how it went against me," he said.
"Amateur boxing stinks from the core right to the top."
The heated controversy led Conlan to question if boxing should be included in the 2020 Olympics.
"The IOC needs to have a look at Olympic boxing and see whether it should even be in Tokyo. If I was a young boxer watching the Olympics, I don't think I would want to be there."