Off games is not the issue for me. Lack of effort is. Very hard to play in CL when 2 players walk around and don't help the team unless they have the ball at their feet. Everybody can have off games, but you have to try all the time. That's how winning is done at this level.
Rest him in some easier games and ask him to run more in CL and give more in terms of effort. Nobody expects him to dribble half the team every game, but when the ball is 2m away from him and he walks unbothered and unwilling to put even a bit of pressure it is upsetting.
I don't think Messi is the first to blame, but he's one of the players who massively underperform in CL quarters in the last 3 seasons.
Sure, I'll be the first one to tell you Messi could have exerted more effort and has underperformed in our CL exits, but look at the state of our team when Messi doesn't play.
It's simply not good enough. Our team is deeply flawed. Barca have been blessed with some great midfielders throughout their history. Xavi, Iniesta, Busquets, Deco, Pep Guardiola, Michael Laudrup and more, and somehow we've managed to put a decent midfielder like Rakitic at that pedestal.
Somehow we've managed to rate Alba so highly when the only reason he's even a footballer is his pace. Take two of our other FBs pace away in Alves and Abidal and they would still be very good. Do that with Alba and you're left with the most useless player in the squad.
The squad is so flawed and overrated that it's unbelievable. On top of that we have players like Suarez who are past their best if you're trying to win the CL that we're still hinging on while contemplating selling or loaning a prospect like Dembele.
Messi can improve his performance and lack of effort, but in games where it doesn't work out for him, everyone else will be left exposed. That wasn't a problem before because the World Class players we had were actual World Class or very good. We've managed to give that tag to decent or average players at best and wonder why everything fall apart when one player is off.