The decision came after a conversation with coach Eirik Myhr Nossum on Sunday evening.
The 28-year-old turned four on Saturday's 15km classic in the Ruka mini-tour.
May be joined by the Ingebrigtsen brothers"I am the third best Norwegian here today, and it will be enough to run the Tour de Ski," Tönseth told the press after the race.
He took silver at the Norwegian Championship in cross country running behind Henrik Ingebrigtsen in October.
In Portugal he can be joined by the other star brothers, Filip Ingebrigtsen in the senior class and Jakob Ingebrigtsen in the U20 class.