The 25-year-old tested positive for cocaine, explaining his omission from the Castleford side that lost 24-6 to Leeds Rhinos in Saturday's Grand Final at Old Trafford.
Hardaker, who was among the nominees for the Super League's Man of Steel award, failed the test following a Super 8s game against former club Leeds on September 8.
A Rugby Football League statement read: "The Rugby Football League can confirm that Zak Hardaker is provisionally suspended from all competition after it received notification from UK Anti-Doping that he had tested positive for a banned substance.
"He will therefore not be considered for the England Rugby League World Cup squad due to be announced on Monday at 12pm. The RFL will be making no further comment until the outcome of the case has been determined."
Hardaker scored 13 tries for Cas in 30 appearances en route to winning the League Leaders' Shield for the first time, leaving him in strong contention to earn a place in England's squad for the World Cup in Australia.