Sydney defender Callum Mills will miss the rest of the AFL season after breaking his foot in an accident after training.

The Swans say Mills was throwing an American football with teammates on the way back from a cafe on Thursday when he tripped and fell.

“It was a really unfortunate accident and unfortunately Callum has an operation on Monday and will be out for the rest of the year – it’s a bad break,” Sydney coach John Longmire said.

“It’s something out of the blue and clearly very disappointing for him and us.”

The AFL’s Rising Star in 2016, Mills has played every game for the Swans this year for a total of 55 appearances.

Mills’ injury has shades of a similar mishap involving backline teammate Dane Rampe at the beginning of last season.

Rampe broke his arm during a morning run near the Swans’ headquarters when he attempted to jump a chain and landed on concrete.

The All-Australian went on to miss seven games.

Sydney have dropped Gary Rohan and added Harry Marsh and debutant Ryley Stoddart for Saturday’s clash with Brisbane at the Gabba.