The problem is not Messi having a bad form, the problem is the rest of the team who despite Messi being marked by 4 players, they cannot take advantage of that situation, something really bad has to happen in order to not exploit that situation and that's why besides Messi almost nobody scores or even assists.
He's marked by 4 players in the centre. The problem is, the other players like Iniesta, Xavi, Cesc, Thiago, Pedro, Villa, Alexis all prefer to attack the centre. So those 4 players that are marking Messi, also come into play to negate the other players.
Either the team should take advantage of the space on the wings(which would also stretch the pitch horizontally and create more space in the centre), or they should play a striker(Villa, Alexis) which would stretch the pitch vertically to create more space in the centre. Or both.