France coach Didier Deschamps was sweating on the fitness of several key players on Saturday as his team battled a mystery virus on the eve of the World Cup final against Argentina.

With little more than 24 hours to go before the world champions face Lionel Messi and Argentina at Doha's Lusail Stadium on Sunday, France have been left reeling by a viral outbreak that is believed to have affected five players so far.

Central defenders Raphael Varane and Ibrahima Konate, and winger Kingsley Coman were the latest players to be laid low by the illness, forced to miss a training session on Friday.

That came two days after Adrien Rabiot and Dayot Upamecano were ruled out of Wednesday's semi-final victory over Morocco.

Players, staff and other sources close to the French squad have spoken of a range of symptoms affecting the team in recent days including fever, stomach pain and headaches.

Both Deschamps and France captain Hugo Lloris said Saturday they had no further medical updates as they appeared at a pre-match press conference just after 11:30 am local time.

"I left quite early this morning from the camp -- they were all still asleep," Deschamps said. "I haven't had any recent updates.

"We are trying to take as many precautions as possible, to adapt as necessary and get on with it. Obviously it would be better if this wasn't happening but we are handling it as well as possible with our medical staff."

Lloris, who also said he had not seen his team-mates early Saturday, added: "We are never really prepared for this type of thing but we are trying to prepare in the best way possible."

The virus threatens to derail France's bid become the first team to win back-to-back World Cups since Brazil achieved the feat in 1962.

- Messi mission -

Standing in their way are an Argentina team led by Paris Saint-Germain superstar Messi, who is looking to cap his glittering career with the one major title that has eluded him.

Anticipation for the showdown between the European and South American heavyweights is reaching fever pitch, with the cheapest tickets on the secondary market changing hands for more than $4,000.

Argentina fans who have flooded into Qatar for the tournament demonstrated for a second day outside a Doha hotel on Friday, demanding their country's national federation help them find tickets for the final.

On Saturday, a Morocco side whose history-making run to the semi-finals caught the world's imagination, have a chance to win the bronze medal.

They will face Croatia, the beaten finalists in 2018, who exceeded expectations in Qatar to reach the semi-finals only to be abruptly halted by an inspired Messi and his protege Julian Alvarez.

Walid Regragui, the coach of Morocco, the first African or Arab side ever to reach the last four of the World Cup, said the third-place playoff "annoys me a little."

"It's always very difficult for the two teams after such a big disappointment as losing a semi-final, to play another match two days later," Regragui said.

"As far as I'm concerned, you are in the idiot's position if you are third or fourth."

However, Croatia forward Andrej Kramaric said his teammates' motivation would be high because winning a medal would "make you a hero for all time" in the country of 3.9 million people.

Sunday's final at the 89,000-capacity Lusail Stadium will bring one of the most controversial World Cups in history to a close.

FIFA president Gianni Infantino shrugged off criticism of the event, describing it as the "best World Cup ever".

"The World Cup has been an incredible success on all fronts," he said at a press conference on Friday.

"The main one being the fans, the behavior, the joyful atmosphere, the bringing of people together. The fans meeting the Arab world, it has been very important for the future of all of us."