Messi missed the 1-1 draw with Eibar on Tuesday with an ankle problem but the Dutchman explained that "he's fine, there's no pain in the ankle. He trained on Dec. 30 and Dec. 31 when the others were off. He's ready, happy and hungry to play."
Messi is now free to negotiate with other clubs after moving into the final six months of his contract at Barça.
However, Koeman called for calm: "We have to look at the situation. He said he doesn't want to make a decision now and we have to respect that.
"Like anyone out of contract, he's free to decide what he does. He's a player that's always given his best to help us win games and I see no problem. We can't be nervous or worried. We have to respect his decision."
With respect to Messi's absence against Eibar, the coach admitted that "there is a little bit of Messi-dependence. His effectiveness and importance for his club is huge.
"I have seen games when the team didn't play well and he makes the difference. There is a reason he's the No.1 in the world."