Messi came in for criticism after Argentina were held to a shock 1-1 draw by Iceland in their opening Group D match , in which the forward missed a second-half penalty.
Failure to beat Croatia in Nizhny Novgorod could strike a damaging blow to Jorge Sampaoli's side in their quest to go one better than in 2014, when they lost the final to Germany.
But Rakitic insists there is no player more proud to represent their country or more determined to get them back on track towards success than his club team-mate Messi.
"My impression is not just that he's motivated, but that he's uber-motivated," he told a news conference. "When he goes to Argentina, he has a special smile on his face. I don't think there is a player more proud to wear the jersey than he is.
"I appreciate him as a human and a player, I've seen the way he has been over the last few weeks, he has given his all and he deserves all our respect."
13 – Since 1966, only Luigi Riva has attempted more shots in a World Cup game (13 vs both Sweden and Israel in 1970) without scoring than Lionel Messi did today against Iceland (since 1966). Shocker. #ARGISL #ARG #WorldCup pic.twitter.com/rhnROlfewx— OptaJoe (@OptaJoe) June 16, 2018
Rakitic admits there are not many secrets about Messi that he has been able to divulge to his Croatia team-mates to help them contain him.
"What can I tell them that they or the whole world doesn't know?" he said. "Messi is one of the best players in the world and he'll have his moments. It's up to us to stop him but to play the right way and enjoy the match."
Rakitic compared Messi's influence to that of Luka Modric, a player he feels honoured to play alongside for the national team.
"It's a privilege to play with both," he said. "They're really different in their style. Leo is essential at Barca, by far the most important player, he plays up front with a lot of flexibility. That's what Modric does as well. He's our captain, he's a character, he leads us.
"If I could pick my starting XI, I'd have both in my team. I'm proud to play with such outstanding players. I repeat again: for me, Leo Messi is the best player of all time and I hope he plays as long as he wants."
Indeed, Croatia's midfield has been described as one of the strongest at these finals, something Rakitic was proud to be told.
"Thank you for the implied compliment!" he added. "We try to be strong as a unit. We want to be sure we pass the ball around smoothly and help our team-mates.
"In a country like Croatia, it's very special to have so many big players at big clubs and we want to transfer these qualities to the national team. We hope we'll be able to do that. It's an important match. If we play together, we'll make things easier for ourselves."