Former Premiership star joins Titans' coaching team
And Burnell says the Sheffield-born former England Saxon is a quality acquisition.
He said: "Jon has just finished playing but he is still registered as a player if we need him.
"He’s been at the sharp end of the game for a long time but coming to help coach here he’s fresh and he’s got some great ideas.
"But the biggest thing is that, like everyone at Rotherham, he wants to be here.
"That’s what I like about this place. I wanted to come here and prove myself and Jon has done the same. At this moment it’s purely on a voluntary basis but he really does want to prove himself and we feel he will bring a lot to the club."
Clarke scored 32 tries with the Saints between 2003-12. He moved to Worcester and spent two years at Sixways before switching to Headingley on loan last season.