The teenager was once again excellent in the good victory over Valladolid, providing an exquisite back flick to allow Messi to run through and score his record-breaking 644th goal for the club.
Messi immediately ran to his team-mate to celebrate and it is obvious to Koeman that this is a relationship that will continue to grow over time.
He said after the contest: "He is a very good player, with a very good connection with Leo.
"He is working a lot, without the ball he is also important in our team. I see him very comfortable in his game. Does he gets on well with Messi? The good guys always understand each other."
Koeman also made a tactical shift here, moving from his regular 4-2-3-1 to three at the back, and the team appeared much more balanced and secure in possession.
The Dutchman agreed that the change offered more protection to his defence, something that has been lacking in recent weeks - but refused to rule out reverting to four at the back if necessary.
He added: "It has given us more security behind by having more people in the midfield between the lines.
"We have seen a very serious team, very concentrated, we have also created many opportunities, but I do not know if I will maintain this system or not."