Sepp Blatter, president of the world governing body, plans to adopt a proposal first mooted by former France captain Michel Platini, according to Sportinformation, a Swiss news agency.
We will experiment with a fourth referee next year
Blatter said the fourth official would operate behind the goals, where he could watch incidents in the penalty area, freeing up the assistant referees to concentrate on enforcing the offside rule.
It was not immediately clear how the official would cover both ends at once.
"We will experiment with a fourth referee next year, following a proposal by Michel Platini, in each of the four major tournaments organized by Fifa," Blatter said.
These are the under-20 and under-17 world championships, the women's World Cup and the Confederations Cup.
Blatter has recently said he also favours a return to a trio of officials of the same nationality because a lack of communication had been the cause of several mistakes.
He had previously backed the need for the best referees, regardless of where they were from.
Blatter also issued a statement on Monday denying there is a conspiracy to keep South Korea in the World Cup.
And he confirmed that the final will be held in Japan, even if South Korea win through.
Allegations of a conspiracy in favour of Korea Republic are dismissed in their entirety
Talk of a conspiracy theory has become increasingly widespread since Korea beat both Italy and Spain in highly controversial fashion.
And the volume of the rumours has now become so loud that Blatter has felt obliged to make an official denial.
His statement issued on Monday said: "Ongoing rumours require me to reiterate the following.
"Any allegations of a conspiracy in favour of Korea Republic are dismissed in their entirety."
The unusual step of releasing such a statement publicly denying the stories shows how high feelings have been running since the shock exits of Spain and Italy.
There have been a string of controversial refereeing decisions during the tournament. Many have been made by the referees' assistants.
But the fact they have favoured the co-hosts so much has set tongues wagging.