Sam Frost ahead of Hawthorn's game against GWS against R21, 2024. Picture: AFL Photos

HAWTHORN has been dealt a massive blow ahead of Friday night's semi-final against Port Adelaide with key defender Sam Frost ruled out for the rest of the season.

The 31-year-old suffered a bone stress injury in Friday night's elimination final win over the Western Bulldogs.

Subsequent scans over the weekend revealed the extent of the injury, with further investigation required to determine an accurate recovery time.

With James Blanck rupturing his ACL in February, Frost has become a crucial figure in the Hawks' rise from 0-5 to the final six in 2024.

The former Greater Western Sydney and Melbourne backman has played every game this season, triggering a contract extension for next season.

Now Sam Mitchell will need to rejig his back six ahead of the trip to South Australia this week.

Jai Serong has been considered the next cab off the rank and been in strong form for Box Hill at VFL level, but Ethan Phillips is more of a like-for-like option.

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The 25-year-old Phillips has played just one AFL game, incidentally against the Power, since being signed late in the pre-season supplemental selection period after Blanck went down.

The 197cm held his own against Port at Adelaide Oval in round 10 when James Sicily missed due to a dislocated shoulder.

Reigning Peter Crimmins Medallist Will Day is unlikely to be available for the clash against the Power, but hasn't been ruled out just yet.

The South Australian hasn't played since suffering a collarbone injury against Richmond in round 23 and is yet to start contact training.