"He has had an ongoing knee problem and it has got to the point where he can't continue," said Tigers director of rugby Richard Cockerill.
"We have had to have the wear and tear repaired and it means he will miss the entire season.
"It is a blow for Craner, who loves playing and just wants to play. It is tough for him as a 25-year-old to be having a year out of the game.
"It is clearly not ideal at this point in time with the World Cup on the horizon to lose someone of his playing ability and his leadership ability.
"We have the likes of Julian Salvi, Thomas Waldrom, Ben Woods and Steve Mafi as back-row options and we will crack on."
The 2001 and 2002 European Champions begin their European campaign this year with a trip to Aironi on Saturday November 12 before welcoming Ulster to Welford Road the following week.