Nicoski, who missed all of 2012 after rupturing a hamstring tendon, had been stepping up his program, but the recovery between sessions had been slow, causing the medical staff to modify his training once again.
The Eagle will be back in round seven at the earliest.
While frustrated with the setback, Nicoski backed the decision, keen to ensure he could compete with 100 per cent confidence when he resumes.
"The medical staff has devised a modified and controlled program for the next eight weeks, which means I would not be ready to play until round seven," Nicoski said.
"I will be placed on the long-term injury list during that period and I look forward to having a positive impact on the West Coast Eagles season after that time.
"There has not been a setback per se, it's just a matter of backing it off a little over the next couple of months, managing and manipulating my training loads."
The club will not immediately elevate a rookie to replace Nicoski on the senior list.
John Butcher is a forward in AFL Fantasy. He did not play in 2012. Register your team at our AFL Fantasy hub.
