A disappointed Juergen Klopp turned off the TV when he heard fans of his former team Liverpool booing Trent Alexander-Arnold, who is set to leave this summer after two decades at the club, during a 2-2 home draw with Arsenal earlier this month.
Liverpool-born Alexander-Arnold, who joined the club in 2004 when he was six, debuted for the senior team when Klopp was the manager.
The 26-year-old, who is regarded as one of the best right backs in the world and can also play as a midfielder, has made 353 appearances for Liverpool, winning the Premier League, the Champions League and the Club World Cup during Klopp's tenure.
"I watched the game when he came on and I heard the booing," Klopp said at a fundraising event for the LFC foundation on Friday.
"I am old so I thought it might be my hearing, so I switched up the volume ... I needed another 10 seconds to realize and I switched the TV off. I honestly couldn't have been more disappointed in this moment. This is not us, 100% not us."
England international Alexander-Arnold also featured prominently as Liverpool won the Premier League again this season under new manager Arne Slot.
Slot earlier said he was not sure if Alexander-Arnold would make his final appearance for the club in Sunday's home game against Crystal Palace, after which Liverpool would hoist the Premier League trophy.
Klopp, who is set to attend Sunday's match, held up an Alexander-Arnold Liverpool shirt to show his support for the player.
Liverpool forward Mohamed Salah, who leads the league's scoring charts with 28 goals, also spoke out earlier in support of his teammate, saying Alexander-Arnold did not deserve the boos.
Klopp said Liverpool fans should not forget what Alexander-Arnold has done for the club.
"I don't tell you, you should not be disappointed, you should not be angry. I tell you, don't forget. This club doesn't forget," he said.
"Every day he gave absolutely everything for this badge ... after 20 years he decided he wanted to go somewhere else. If somebody should be angry about this, it's the owners, but they're not."
