A draw with Atletico Madrid on the final day of the season saw the title slip away from Barcelona, but Messi admits that it was also a difficult campaign on a personal level.
"It was a tough year and it has not been the best for me," the Argentine told Mundo Deportivo. "A big team is obliged to win titles and this year we accomplished nothing.
"It was kind of the whole group, though, not just individuals, but it was a let-down for the whole team."
"We would have liked to have become champions for ourselves and for the manager - he deserved it," the 26-year-old added.
Barcelona agreed terms with Messi on a new deal earlier this week.