The former Crusaders, Leinster and Highlanders forward joined the Premiership Tigers last August, and went on to become the oldest captain in the club's history earlier this season.
"I had a few niggles but otherwise I've been really pleased with how I've played here and my body feels really good," he said.
"But it's just got to a stage where mainly I'm just playing here because I want to play."
Thorn has long stuggled with the idea of retirement, and recently told the Leicester Mercenary that he couldn't even say the word.
"The hard part about discussing the 'R Word' is that my body is not broken. I am really enjoying my rugby and feel like I am really contributing. So it's not easy. When your body is broken and you are not performing, it must be easier.
Brad Thorn's 21-year career
1994: Makes debut for rugby league side Brisbane Broncos.
2001: Switches codes and joins Crusaders.
2002: Takes a year out of the game before rejoining Crusaders and making his All Blacks debut a year later.
2005: Goes back to league, rejoining Broncos and making 70 more appearances for the club.
2008: Switches back to union again in 2008 and wins the World Cup with New Zealand in 2011.
2014: Joins Leicester Tigers, becoming the oldest captain in club history against Saracens.
2015: Announces retirement aged 40.
