The Catalan giants produced a below-par display and Messi was on the periphery of the action for much of the game, striking a post in the first half but producing precious little else.
The forward doesn't have an open-play goal for Barcelona yet in the league this season, his solitary strike coming from the penalty spot against Villarreal in the opening round.
And while Koeman admitted that he thinks Messi could be performing to a higher standard, he is not concerned that this could be a long-term problem.
He said ahead of Tuesday's Ferencvaros clash: "Maybe Messi's form could be better at this moment, but he's happy, he's training well, he's focused, he wants to play and he wants to be captain of the team and he's improving. I haven't got any complaints.
"There is always pressure to win games as a player or coach at Barcelona. We know the club's situation; there are things outside the pitch that we can't influence.
"He also had bad luck with the ball that hit the post and with the final play of the match. Normally, he puts it between the posts! I have no doubt about his form and we'll see that in the coming games."
Barcelona appeared particularly toothless in the loss to Getafe despite finishing the match with five attacking players - Messi, Philippe Coutinho, Ansu Fati, Francisco Trincao and Martin Braithwaite.
But Koeman isn't stressing over the attacking potency of the team and is sure that once the team finds a settled rhythm, they will come good.
He added: "I'm not worried because we've scored eight goals in four games and I don't think many teams have done that. It's normal that, against Sevilla and Getafe, it's more difficult to create chances.
"I'm not disappointed with the players. I see a happy team. I can never be disappointed with a player who works their hardest."