Messi scored in the 3-0 win.
Asked if Messi will stay, Koeman replied: "It's a question for Leo, not for me.
"I see Leo happy, he is working, he is important in our game, with his creativity. It shows if there are good players by his side.
"Each team needs people like him and the others to create danger ahead."
He added: "In principle I am very happy with the work we have done. At the end of the game there are mistakes with the ball. The team was very involved from the beginning of the game.
"We have done the work to defend. The team has gone to score more goals. We have scored three. It is a good number but we have created more."