Late in the first half of that opening leg at Camp Nou saw Messi come into contact with Andy Robertson along the sideline. Off balance, Milner came in late with a shoulder barge on the Barca talisman, sending Messi to the ground.
Incensed over the late contact, Messi called for a yellow card to be handed out but Milner escaped a warning on that occasion.
Having been embarrassed by a Messi nutmeg back in 2015 when he was a member of Manchester City, the Argentine believed it was an attempt at payback.
“He wasn't happy,” Milner, who is learning Spanish, told the Daily Mail. “He was giving me plenty in Spanish going down the tunnel at half-time as well. He was calling me 'burro'.
“It translates as donkey but I think it's also used in Spanish football as a general term for someone who goes around kicking people.
“I asked him if he was all right, but he wasn't having it. I don't think he realised I understood his Spanish.
“He said: ‘That foul you did, that's because I nutmegged you’. I left him to it at that point and went into the changing room.
“Look, I've only got admiration for him. He has earned the right to say what he wants.”
Milner admitted that given Messi’s skill, that level of physicality is required in order to help get him off his game.
However, the midfielder also noted it’s staying within the limits – his intention was never to hurt Messi.
“The stuff he did in that game, stuff he has done his whole career, it makes him tough to play against,” Milner added. “If you try and stop him, you can't be scared of being made to look foolish. I've done it.
“I've been nutmegged by him and it has been viewed a million times. I wasn't the first and I won't be the last. He's an incredible player.
“But with players like that, you have to let them know you're there and not let them have everything their own way. You just need to try to disrupt their rhythm.
“You don't want to hurt him but it's a physical game and, if he's running the game, you try and knock him out of his stride. It's part of the game, the mental side.”
While those efforts weren’t rewarded in the first leg, which saw a 3-0 Barca victory, a stunning comeback at Anfield saw Liverpool emerge 4-0 winners to advance to the final.
And Milner, who was overcome by emotion at the final whistle, believes the quality of opposition, combined with the injury absences of Mohamed Salah and Roberto Firmino, made it a night to remember.
“Messi's an amazing player and the special thing about the night was to turn it round against a team like that with the best player in the world in there and Luis Suarez and Gerard Pique, too,” Milner said. “There are not many teams in the world that could turn around a deficit like that with two of your star players gone. It was such a team effort.”