Ronaldo, 36, has scored 10 goals in just 14 games since making his return to Old Trafford, six of which have come in the Champions League.
His goal scoring form has been vital in helping United through what has been a difficult season. The club currently sits eighth in the Premier League table and has won just one of its last six top flight games – form that resulted in manager Ole Gunnar Solskjaer being sacked last week.
“Cristiano already knew the club but that was at a different stage and now he has adapted in an impressive manner,” Messi told Marca of Ronaldo’s United form.
“From the start he has scored goals as he always does and had no problems adapting.”
Messi and Ronaldo have dominated world soccer for more than a decade and their rivalry while playing for Barcelona and Real Madrid was one of the most competitive in the sport’s history.
During the nine years they shared in La Liga, both propelled their teams to great success and scored a combined 922 goals.
“Time has passed since we competed in the same league,” Messi said.
“We not only competed on an individual level but also on a team level for the same aims. It was a very beautiful stage for us and for people because they enjoyed it very much.
“It’s a beautiful memory that will remain in football history.”
Messi: “I will return to Barcelona one day.”
However, he has not ruled out a return to the Catalan club.
“I always said that at some point I will return to Barcelona because it is my home and because I am going to live there,” he told Marca.
“And obviously if I can contribute and help the club I would love to come back.”
Messi also took time to praise his old teammate Xavi, who took up the managerial reigns at Barcelona this month.
“[Xavi] can contribute a lot. He is a coach who knows a lot, knows the place perfectly and has lived in Barcelona since he was a child,” he said.
“He has brought back hope to Barcelona because he is a highly respected figure among the fans and the players. He will be a very important coach for the younger players because he is going to teach them.
“With him, the team will grow a lot. I have no doubt.”