The 21-year-old midfielder was hurt in a tackle during match simulation at training last week and further medical assessment has confirmed surgery is required.

The setback is a blow to the Blues' hopes of climbing back into finals contention under new coach Michael Voss this season.

But they are hopeful the body of work Walsh has put together over summer will hold him in good stead for an early-season return.

"It is obviously disappointing news for Sam," Blues football boss Brad Lloyd said.

"He'd completed every session so far over the summer but unfortunately these incidents are a part of footy.

"Sam will throw everything into his rehab and his teammates will continue to do the same for the start of the season."

Walsh, the No.1 draft pick in 2018, has played all 61 possible games with Carlton since being drafted and was named an All-Australian for the first time last year.

He was rewarded with a bumper new four-year contract this month, which ties him to the Blues until the end of 2026.

Walsh has also been elevated to joint vice-captain with Jacob Weitering in a streamlined leadership group alongside captain Patrick Cripps.

"Sam leads from the front with his professionalism and commitment every day he walks through the doors of the footy club and there's no doubt he will take the same approach to his recovery over the coming weeks," Lloyd said.

"We'll continue to assess Sam throughout his recovery, at this stage we expect him to be available to play again after the first month of the season has been complete.

"There has been some real competition for spots in that midfield group over the summer so we look forward to seeing who puts their hand up and takes their chance over the coming weeks."

Carlton have pre-season games against St Kilda and Melbourne in coming weeks before a round-one showdown with traditional rivals Richmond at the MCG on March 17.

Australian Associated Press