Koeman hit the headlines following Saturday's Liga defeat to Getafe with some guarded words of criticism against his captain, who four days earlier had played 90 minutes in the altitude of Bolivian capital La Paz as he helped Argentina to victory in the World Cup qualifier.
“Maybe, right now, Messi’s performances could be better,” Koeman told reporters ahead of the Champions League clash against Ferencvaros.
“But he is happy, he is working hard and he wants to be the captain of this team.
“I do not have a single complaint. He has also had some bad luck. He hit the post and in another game that will be a goal. I don’t have any doubts about his performances and we are going to see him back to his best in the games to come, I am sure.”
Messi responded by opening the scoring from the penalty spot in Tuesday's 5-1 thrashing of the Hungarians, while 17-year-old pair Ansu Fati and Pedri also hit the headlines by both finding the net for the Blaugrana at Camp Nou.
The Argentine contributed an assist for Ousmane Dembele's late goal to round off the rout and posed a constant threat across the 90 minutes, prompting Koeman to praise his performance.
"If he plays like he did tonight, I will have no complaints over Leo," the Dutchman told reporters after the final whistle.
"He worked hard, he scored from the penalty spot but I then I too used to score penalties. If he doesn't score but gives two or three assists we cannot ask more of him.
"We have people up front playing well and that is the best thing for a coach. I think we have shown that we have great players up front.
"With a great Leo, with two assists, and that is why we leave here happy. There is competition and not just for the right wing. We can play differently with Leo out wide or at No.10. There are great players in attack."
Messi and Barca will be back in action on Saturday, when they host Real Madrid in the first Clasico of the 2020-21 season.