The Ireland international centre was forced to retire from the game recently, at the age of just 26.
This was as a result of injuries sustained to his eye during an assault outside a Wigan nightclub, earlier this year.
“I’m sure he will succeed in anything he puts his mind to,” Sandercock told the Hull Daily Mail.
“Sean has a great enthusiastic personality.
“I’m not sure what he’ll do next.
“Obviously, the news will take a while for him to absorb.
“Sean will then have to make some decisions after the news sinks in.”
Gleeson’s time at Rovers was marred by injury. A back problem ruled him out of the first four months of last season, while a knee injury also affected his progress in east Hull.
Sandercock regretted that the KR fans never got to see a fine player at his peak.
“It’s a tragedy that Sean has had to retire, but it’s outside of Sean’s control,” he said.
“He hasn’t been able to play much for Rovers the last couple of years.
“I’m disappointed because he is a class player and a first class trainer.
“He was willing to learn and his enthusiasm was infectious. He will be a big loss for us.”