The Argentine star was noticeably agitated during television interviews following a shock 2-1 defeat against Osasuna at the Camp Nou where Messi struck a sumptuous free-kick to level the scoreline just after the hour mark. For Messi, the result was symptomatic of a subpar season.
"All season we have been a very weak team, beaten for intensity, for motivation, people can score against us very easy, we lost many points where we shouldn't lose them," Messi said post-match, courtesy The Athletic's Dermot Corrigan.
"This game has just summed up how our season has been."
Real sealed the title with Thursday's late victory against Villarreal, marking a 10th consecutive win since the restart for the capital city side. Barcelona dropped nine points over that stretch after leading the league upon the resumption of play in mid-June.
"Madrid did their own job well, did not lose any games after the break, they deserve praise," Messi said. "But we did plenty for them to take this league, dropping many points we shouldn't have. We have to be self-critical, starting with the players, but in all areas."
Facing the prospects of a rare trophyless season, Messi warns that Barcelona will lose the second leg of the last-16 Champions League clash with Napoli if things don't improve.
"I said before that playing like this we would not win Champions League, not even enough for La Liga. To fight for UCL we will have to change so much or we will lose against Napoli too.
"But we must change a lot, and there must be a lot of self-criticism."
Messi, who is reportedly discontent with the management of the club, also cites past Champions League failures against Roma and Liverpool as a reason for restlessness among supporters.
"Fans must be very angry at how this whole season has gone, that is normal, we are too, its logical. We were also coming from defeats at Roma, Liverpool, people don't have patience, and it's normal, considering everything," Messi added.