Messi, 33, was suspended for the wins over Cornella and Elche but is available again having served his two-game ban for his Supercopa red card.
"Leo is always hungry to play and to win things," Koeman said of Messi's return. "He's used to winning trophies. He's a winner and wants to play every game."
Messi missed the Supercopa semifinal with an injury but returned for the final defeat to Athletic and Koeman says he's not suffering from any problems.
The Barça coach added: "He had a slight injury before but he is eager to get back in action after his ban. He's fresh and he doesn't have any fitness issues. To win things we need Messi in form."