Infantino also said he would be happy for several countries to share the hosting of the World Cup, describing it as much a "social event for the whole world" as a global sporting competition.
Infantino made a 40-team World Cup a key part of his campaign before his election in February but admitted it was not entirely up to him to decide whether the 2026 finals should be increased from the tournament's current 32-team format.
"My opinion has not changed on the 40 teams, but that's my opinion. We will have to discuss it and see what's the best for football," he told reporters from international news agencies on Tuesday.
FIFA expects to make decisions by October on the number of teams, the format for the tournament and the continents that will be eligible to stage the tournament.
The latter would be a key decision as it would determine whether countries from Asia, where Qatar is staging the 2022 World Cup, can bid to be hosts.
The final decision on the host nation will be made in May 2020.
"For the moment, everything is open, but there is a question of who can and cannot bid...we will see," Infantino said.
"CONCACAF (North and Central America and the Caribbean) didn't have a World Cup for a long time.
"Nothing is definite. I believe in the 40 teams because I think it is positive for the development of football and we have seen that again at the Euro 2016 in France with eight more teams.
"We need to realise that these kinds of events, like the World Cup or European Championship, are more than just a competition, they are really social events for the whole world."
Speaking about the number of countries who could potentially share a tournament, he said there were "no limits to whatever is good for football."
"What is important is that the whole process is done in a correct way, a transparent way," he added.
(Writing by Brian Homewood; Editing by Ian Chadband)
