#1 He does not have the crowd to inspire him and his team at away games
Messi might not be able to motivate his teammates at times, but the Barcelona faithful at the Camp Nou could always replace him to do the task in cheering the players. This critical factor might be the reason why the Catalan giants' home and away form has been so different in the Champions League.
At home, they have beaten almost every team they faced in the competition with a considerable margin. They hammered Manchester United 3-0, Lyon by 5-1 and Inter Milan 2-0 at the Camp Nou but could not win against the last two teams when they played in their respective home grounds.
Travelling to another country to play the away matches has pushed Barcelona away from their home support and eventually gave them even more pressure in the away games.
Ronaldo, on the other hand, had been somewhat more motivated when the crowd have been against him. He even had the opposite fans cheering for him when he scored from an overhead kick against Juventus last season. Overall, Ronaldo's mentality at away games is arguably much better than Messi's.