The Catalans' struggles this season worsened on Tuesday evening as they slumped to a 1-1 draw with Eibar in the absence of captain Lionel Messi, leaving them still some way adrift of Atletico Madrid and Real Madrid.
"I'm realistic, winning the title is complicated," Koeman said after the game.
"Nothing is impossible, but we have to recognise the distance.
"Atletico look very good to me. They're very strong and they don't concede many goals."
"I don't want to say that we lacked experienced players," Koeman said.
"There's a transition in the team and we have injuries too.
"We're playing young players, but today we had five or six young players and players with experience too.
"We missed Leo, who makes a difference, but the feeling now is that we should have won.
"We had chances, missed a penalty and gave away the goal, which was their only shot on target."