The Catalan giants finished last season without a trophy, which signallled the end of Quique Setién's tenure at the club.
With the club having already missed out on one trophy this season after losing to Athletic Bilbao in the Spanish Super Cup final, Koeman admits trophies will be hard to come by right now.
"I have said several times that this is a season where we are changing things, we are opting for young players," Koeman told reporters, as per Goal.
"Barcelona are not about to win a lot of things right now.
"We have to be realistic about where we've come from, the changes we've made... not everything depends on one player. We always have to be ready to fight, but we have to be realistic.
"We know our situation in La Liga, it's complicated."