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.
“They’ve got a bigger problem with Brodie Grundy than they have with any other player on their list,” King said.
“He 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.
“We don’t say that any more.”
Collingwood’s close loss to Brisbane on Friday night prompted further questions about Grundy’s recent performances, led by Hawks great Dermott Brereton
“He’s injured or he’s hit the wall,” Brereton said.
“He has rucked unchanged for three years, a couple of minutes here from various players, Cox if he’s in, but we’re talking a couple of minutes.
“We’ll hear at the end of the year he’s carrying an injury or he’s hit the wall.”
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.