Kennedy was tipped for great things when he broke through into the Hoops side at the start of the millennium.
But he was never the same after sustaining a serious knee injury in a challenge by Romania’s Ionel Ganea just 14 minutes into his Scotland debut at Hampden Park in 2004.
Kennedy is now part of Rodgers’ backroom staff and the Northern Irishman was reminded of his early retirement at 26 when he watched a re-run of a tackle by Ryan Bowman on left-back Kieran Tierney in last week’s 2-0 win over Motherwell at Parkhead.
In Rodgers’ view, teenage Hoops defender Tierney was on the end of an “horrendous” challenge.
Ahead of the home game against Hamilton on Saturday, where the runaway Ladbrokes Premiership leaders look to extend their unbeaten domestic run since the start of the season to 32 games, Rodgers said: “My only worry at this moment in time is protection for my players.
“I have seen two tackles in the last two games that weren’t good tackles at all.
“And we are a team that can play any type of game. We have come through physical games and footballing games, tight games. My players never complain or moan, they get up and get on with the game.
“We respect referees but I would like them to have a wee bit of protection for players.
“I’ve seen a tackle on Kieran Tierney which I didn’t see right after the game but I watched a replay afterwards and it was an horrendous challenge.
“This is a kid who is 19, one of the great prospects of Scottish football.
“I have a boy who is a brilliant coach on my staff, John Kennedy, who was also a brilliant prospect who in one challenge lost his career.
“I don’t really want that to happen to any of my players or any player for that matter, whether they are from Celtic, Rangers, Hearts, Hibs or wherever.
“We need to ensure they are protected.
“I understand there is a maybe a dimension of ‘you have to get tight to Scott Sinclair, got to put in a challenge to Kieran Tierney or James Forrest or whoever’.
“But it is the responsibility of the referee to protect the game and the players because I said it was an horrendous challenge and the week before against Inverness, Scott Sinclair had an awful challenge on him.
“If we are trying to get the best players playing here in Scotland they need a little bit of protection.”
Asked if teams maybe felt that the physical approach was the only way to stop his side, the former Swansea and Liverpool manager said: “We are a team of men.
“We have young guys in the team but we are playing a man’s game so we have no problem with the aggression and we have coped with that at places like Aberdeen, in a really tough physical game, tough challenges, fair challenges.
“The concern for me is the challenges that are late, that like last week was a straight-leg challenge which could have really damaged him.
“If Kieran’s foot was planted you could be talking a different story about one of the great talents in Scotland.
“Now that is the duty of the referee, to protect them and protect the game.”