The Catalan outfit had to battle back to secure a 1-1 draw at Athletic Bilbao on Saturday evening, with Memphis Depay netting the equaliser.
The Dutch tactician feels the rest of LaLiga feared his side more when the Argentine superstar was in the team.
“I don't like to always talk about the same thing, but we're talking about the best in the world," the Dutchman told his post-match press conference.
"Our opponents were more scared when Messi was here.
"For us as well, if you pass the ball to Leo, usually he won't lose it. You can tell [Messi] isn't there. We know that and we can't change it."
Koeman felt the draw was a fair result on the night, which he wasn't too unhapp with.
"I think we made things too difficult for ourselves at the start of the game. We need to know when we can play short, from the keeper as well. We weren't calm enough in the first 15 minutes.
"I think a draw is a fair result, we had chances to win, Athletic were at a very high level. Playing like that, this is a very tough ground, so I can't be unhappy with the result."