Philippe Coutinho said it was hard to explain why Lionel Messi and Barcelona had not won the Champions League more often in recent seasons.
Messi, 31, is a four-time winner of Europe's premier club competition, but the last of those successes came in 2015.
Barca have been eliminated in the quarter-finals of the Champions League in the past three seasons.
Asked why Barca, with one of the all-time greats in Messi in their side, had struggled for success in the competition in recent seasons, Coutinho said that was tough to explain.
"That's difficult to say. Messi is the best player in the world, perhaps the best in history and it's difficult to explain that," the attacker said ahead of Barca's clash against PSV on Tuesday.
"I guess there's no explanation to that. Such as all of us he is aiming so much to win big things and the Champions League is one of them."
Barca host PSV in Group B, which also includes Premier League outfit Tottenham and Serie A giants Inter.
