The hard-working forward has a severe injury involving the hamstring group of muscles at the back of his right leg.
Shackleton had emergency surgery on the day following his injury to repair the damage, and will remain in hospital for a period as the leg needs to be immobilized following the surgery.
It is unlikely the 27-year-old will be returning to the field this season. Shackleton joined the Parramatta Eels from the Sydney Roosters late last year and was one of the best trainers throughout the Eels’ pre-season.
A replacement will be named tomorrow when coach Daniel Anderson announces his team for the Eels’ second-round blockbuster against the Manly Sea Eagles at Parramatta Stadium on Sunday.