No doubt that Messi is one of the Greatest of All Time, but to be The Greatest he has to be tested in very difficult situation. A great sportsperson is not just about skills, talent and physical hardwork, he/she has to be mentally and emotionally strong.
At times your whole country will be against you, your own fans will start doubting you and all your skills, talent and past achievements will be like of no use., these times will mentally drain you off.
So Messi if presented with this great opportunity, If he can overcome all the negativity against him and just clear his mind and play the way he normal does, no matter how many opposition players are marking him or how weak his team is or if his own goal keeper giving away free goals, he can truly produce a spectacle against Nigeria in the upcoming match.
He might have lost 3 straight important finals for his country, but The Greatest one will not be bothered about pasts, he/she will try and try and keep trying.
Yes, just a win over Nigeria will not prove much here, but it will certainly prove a point and who knows what can happen in later stages.
P.S- Personally I like C. Ronaldo as well, but Messi comes first.