Messi then changed his mind a few weeks later and confirmed he will stay another season at the Camp Nou, although his contract runs out next year.
While his long-term future remains undecided, Koeman has had nothing but praise for his captain since returning to the team.
"From day one, Leo has trained and played well and has given the maximum for the club, for his team and for his team-mates and I have had no complaints about him on any day," Koeman told reporters, as per Sky Sports.
"He proved himself once again the other day against Celta, he pulled his weight as a captain, he helped the team play the ball out from the back because it's so important to keep the ball when you have one less player.
"There's no debate, for me he has always been the best player in the world, I thought that before from the outside and I think it even more now I'm working with him. He's fully committed, he's an example to everyone as a captain should be."