Former Manchester United midfielder David Beckham described Keane as 'one of the most inspirational captains I have ever played with'.
"He is a player who will lead from the front and get a team going," the England captain told PA Sport.
"He is also a player who will tell you when you have done something wrong and something right. You know where you stand with him, he'll tell you in his own special way."
Beckham was eager to stress the importance of Keane's role at Old Trafford, adding: "I think he had one of the biggest impacts on a club anyone could have. The players responded to him in every game.
"I am shocked he has left because I thought he would be there for a few more years, but he has made his decision and everyone will respect that.
People now have to look at what he has done with Manchester United because in the last 12 years he has won everything there is to win in club football.
He has done it gaining respect from so many players that he has played with and against.
Beckham conceded he had no idea what the future would hold for Keane.
"I don't know what his plans are," said Beckham, now at Real Madrid.
He continued: "I hope he'll play for a few more years. Whether he finishes playing or carries on I don't know. I said last week he could become a manager, not right away, because it is difficult when you are as young as he is, but I believe his potential in going into anything and succeeding is high.
"Maybe he'll just spend time with his family. He's a family man and has a lovely wife and kids."
