Vegemite has playfully exposed the questionable eating habits of US tennis star Taylor Fritz's influencer girlfriend after she ate an entire mouthful of the iconic Aussie spread on Instagram.

Morgan Riddle has been a highlight at Melbourne Park, keeping plenty of fans entertained with her eye-catching courtside outfits.

She turned heads last week after betting her boyfriend she would eat a 'jar of Vegemite' if he won his match against seventh seed Stefanos Tsitsipas.

Fritz did his part, winning in four sets against the 2023 Australian Open finalist. 

A hilarious video uploaded to Instagram followed, showing Riddle struggling to eat a spoonful of Vegemite - with no bread or butter in sight.

Seconds later, Riddle gagged at the unique taste and ran out of frame to spit it out.

'That was disgusting,' she said after coming back on camera to drink a sip of kombucha.

'If anyone had to eat a whole jar of that, nope.'

In a light-hearted message, the iconic Aussie spread has hit back at the American influencer, questioning why Riddle make the rookie mistake of eating Vegemite on its own.

'If you're going to do it, at least do it right. Australia, thoughts?' their social media team posted on Tuesday night.

She soon responded, posting: 'Sourdough bread with heaps of buttah?' 

Riddle got the ball rolling last weekend after she shared the bet with her 220,000-plus Instagram followers.

'If @taylor_fritz wins again, I'll eat a jar of vegemite on [Instagram] live,' she captioned a post of her posing outside Rod Laver Arena with a red Chanel bag.

Hours later Fritz - whose tournament ended after he lost to Novak Djokovic in the quarter-finals on Tuesday - was presented with a large jar of the national spread courtside.

Riddle showed she is a good sport when she was filmed in the stands with a grin on her face, clearly accepting defeat.