PORT Adelaide's already decimated ruck stocks have suffered a further blow, with young tall Dougal Howard limping off the ground against Fremantle with a serious knee injury.

The 20-year-old is feared to have ruptured the anterior cruciate ligament in his left knee after colliding into Docker Michael Walters in the third term, with an exact prognosis to be known following scans.

Howard has provided back-up to makeshift ruckman Jackson Trengove in recent weeks with first-choice ruckman Matthew Lobbe sidelined since May due to a PCL injury and Paddy Ryder serving his year-long doping ban.

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North Melbourne defender Luke McDonald had a sore left hip and returned to the field, only to injure his left hamstring in a chase-down tackle of Hawk Cyril Rioli in the second quarter.

McDonald now joins fellow defender Sam Wright (ankle) and tagger Ben Jacobs (foot) on the club's mounting injury list.

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Geelong midfielder Josh Caddy left the ground in the hands of trainers with a left medial ligament injury after Bulldog Jack Macrae crashed into his knee in the final quarter.

Caddy was on crutches after the game and will have scans to determine the severity.

Josh Caddy in pain after hurting his knee. Picture: AFL Media

Brisbane Lion Ryan Harwood's game against West Coast ended in the first quarter after the defender hurt his left knee in a tackle from Eagle Jack Darling.

Lions coach Justin Leppitsch said it appeared to be a posterior cruciate ligament injury, but the severity will be known in coming days.

Meanwhile, the Lions coach also said midfielder Tom Bell, who did not play against the Eagles due to a knee issue, will require surgery that will likely see him miss the rest of the season.

Fremantle forward Tanner Smith injured his left hamstring while being tackled in the third quarter and had ice strapped around his affected leg for the rest of the afternoon.

In other injuries at the weekend:

- GWS co-captain Phil Davis went down with a left foot complaint in the first quarter against Essendon. The 25-year-old underwent a mini fitness test during the quarter-time break and battled manfully in the second half. Davis will be further assessed in the coming days.

- Giant Nick Haynes and Bomber Orazio Fantasia were involved in a heavy collision on the outer wing in the latter stages of the third term, but both managed to play out the game after a spell on the bench. Haynes appeared a little worse for wear from the incident with a back complaint.

- Midfielder Daniel Wells sent a scare through the Kangaroos' camp after rolling his left ankle late in the second term. The 31-year-old, who has had a bad run with Achilles tendon issues over his career, had his ankle taped and returned to the ground.

- Eagles midfielder Matt Priddis was left with a broken nose after receiving an accidental elbow from Lion Tom Rockliff in the first quarter. Priddis had his nose re-bandaged a couple of times throughout the match, but managed to get through.

- Young Lion Tom Cutler experienced hamstring tightness against the Eagles but returned to the field.

- Bulldogs forward Jake Stringer looked in obvious pain while having his left thumb taped midway through the final term against the Cats.