The Blaugrana opened their La Liga campaign with a 4-2 victory over Real Sociedad last weekend but had to settle for a point against Athletic Bilbao at the San Mames Stadium on Saturday.
Memphis Depay rescued a point for Barcelona fifteen minutes from time after Inigo Martinez had given the hosts the lead early in the second half.
Messi ended a 21-year association with the Blaugrana earlier this month and signed a two-year deal with Paris Saint Germain after saying goodbye in a tearful press conference.
“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."
Messi made 778 appearances for Barcelona after making his debut in 2003 and is the club’s all-time top scorer with 672 goals. He won 35 trophies with the club including four UEFA Champions League trophies and 10 La Liga titles.
Barcelona will hope to put things right when they host Getafe next weekend.
