Brunel initially named a young group of 31 plus six reserves on June 18, more than three months before the start of the tournament in Japan, leaving out Mathieu Bastareaud and Morgan Parra entirely.
But having since worked with the extended squad of 37 and made various changes for injuries, while beating Scotland at home and losing away in back-to-back warm-up matches, Brunel is still pondering his options.
Les Bleus host Italy on Friday in their final match before heading to Japan, where they begin their campaign with a tricky test against Argentina on September 21.
Brunel said on Wednesday: "I do not have the 31 for the World Cup yet. We will see this weekend what will happen.
"There are still players who are very close to each other. There are uncertainties. I also hope we will not have any injuries after the match against Italy. I will take everything into account."
The coach revealed his main issue will be selecting players for the back row, with Charles Ollivon and Francois Cros - two reserves - both impressing.
"This is obviously the thorniest area. We have seven players for five places," Brunel said. "This is where it's going to be the most complicated.
Vendredi soir, le #XVdeFrance affronte l'Italie pour son dernier match de préparation avant la Coupe du Monde ! Voici votre équipe pour cette rencontre au @StadeFrance! #FRAITA #NeFaisonsXV #RWC2019 pic.twitter.com/x2A4vKlwR1
— France Rugby (@FranceRugby) August 27, 2019
"There will be painful choices to make, difficult, like every World Cup. This is a very special moment, we will have to do it, we will see according to what will happen during this last match.
"I do not have a fixed idea. [Louis] Picamoles plays big, like [Wenceslas] Lauret and [Yacouba] Camara. There is competition to start.
"There were two substitute players, namely Ollivon and Cros, who they showed that they wanted to compete for a place in the World Cup. It is up to the three starters against Italy to show that they have a role to play."
Paul Gabrillagues looks as though he will make the squad after World Rugby reduced his ban for an incident against Scotland from six to three matches following appeal.
"Paul has the opportunity to be on the list for the World Cup," Brunel said. "Yes, he will not be able to play the first match against Argentina.
"It is a handicap, but it is not insurmountable. The six-week sanction ruled him out entirely."
France XV to face Italy: Maxime Medard, Yoann Huget, Sofiane Guitoune, Wesley Fofana, Gael Fickou, Romain Ntamack, Antoine Dupont; Jefferson Poirot (captain), Camille Chat, Rabah Slimani, Arthur Iturria, Romain Taofifenua, Wenceslas Lauret, Yacouba Camara, Louis Picamoles.
Replacements: Guilhem Guirado, Cyril Baille, Emerick Setiano, Felix Lambey, Francois Cros, Baptiste Serin, Virimi Vakatawa, Thomas Ramos.