Star Hawthorn midfielder Will Day will miss up to four months with a foot injury in a major blow to the undefeated Hawks.
One of the key members of the 'Hollywood Hawks', Day will have surgery after scans revealed a stress fracture in the navicular bone of his foot.
The 23-year-old missed the early part of last year, then was forced to sit out Hawthorn's two finals because of injury.
But Day had put together an impressive start to this season, led by a best-on-ground performance in the Opening Round win against Sydney.
"In this instance, surgery is required to fix the fracture," Hawthorn doctor Liam West said.
"Additionally, surgery will also reduce the risk of future issues for Will during his career."
Hawks football boss Rob McCartney described it as a "bitter blow".
"Will is one of the most determined and resilient young individuals I know, and these attributes will come to the fore as he starts his rehab journey," McCartney said.
"With the knowledge and expertise in our medical team I am confident Will can return to the park before the end of the season."
Hawthorn (4-0) sit atop the ladder heading into their Gather Round blockbuster against Port Adelaide on Saturday night.
Meanwhile, St Kilda forward Max King will seek further assessment on his troublesome knee that the Saints called a "slight setback".
King hasn't featured since round 16 last year due to ongoing knee issues and his return date remains unclear.
The Saints, however, could regain captain Jack Steele for their clash with GWS on Sunday.
Steele (knee) has missed the past two weeks, including Sunday's rousing 17-point win that ended Port Adelaide's long-time stranglehold over them.
At Adelaide, gun Crows midfielder Izak Rankine could be forced to miss Thursday night's clash with Geelong due to a calf issue.
Rankine, who was central in the Crows' controversial one-point loss against Gold Coast on Saturday, has internal bleeding in his calf after sustaining a knock during the match.
Brisbane premiership defender Brandon Starcevich has returned to running as he recovers from a third concussion in 12 games.
Starcevich suffered another head knock in the Lions' round one win over Sydney.
Teammate Kai Lohmann will sit out another week and miss the match against the Western Bulldogs as he manages a persistent ankle injury.
