Star Collingwood ruckman Brodie Grundy's decline in form is becoming a serious worry according to Fox Footy analyst David King.

Grundy, a two-time All-Australian ruckman, has had one of the biggest form declines in the competition, according to the Official AFL Player Ratings.

He was ranked the third-best player in the AFL last year, but now is ranked equal 34th.

โ€œTheyโ€™ve got a bigger problem with Brodie Grundy than they have with any other player on their list,โ€ King said.

โ€œHe was a dominant force. A dominant force. He was the reason why you thought, this game will be separated because of this midfield, and largely because of Brodie in the ruck.

โ€œWe donโ€™t say that any more.โ€

Collingwood's close loss to Brisbane on Friday night prompted further questions about Grundy's recent performances, led by Hawks great Dermott Brereton

โ€œHeโ€™s injured or heโ€™s hit the wall,โ€ Brereton said.

โ€œHe has rucked unchanged for three years, a couple of minutes here from various players, Cox if heโ€™s in, but weโ€™re talking a couple of minutes.

โ€œWeโ€™ll hear at the end of the year heโ€™s carrying an injury or heโ€™s hit the wall.โ€

Grundy signed a seven-year contract extension with the Pies worth roughly $1 million-per-season last year.

He capped a stellar 2019 with an All-Australian selection, his second nod in as many years.