PORT Adelaide youngster Jake Patmore is set to miss the entire season after rupturing the anterior cruciate ligament in his left knee.

The untried 20-year-old midfielder will undergo a knee reconstruction after coming to grief while playing for Port in an SANFL practice match against South Adelaide at Noarlunga on Friday night.

Patmore landed awkwardly after marking on a lead in attack in the second quarter. Play stopped as he was stretchered from the field.

The seriousness of the injury was confirmed on Saturday.

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"This is a terrible blow for Jake, who had been developing well after his second pre-season," Port Adelaide football manager Chris Davies said.

"But we know he is a resilient young man and everyone at the club will support him through his rehabilitation."

Recruited from WAFL club Claremont with pick 58 at the 2017 NAB AFL Draft, Patmore last year played 18 SANFL games and kicked 16 goals.