UPDATE: Wednesday, Nov. 13, at 12:20 p.m. GMT
John Edwards of the Daily Mail quotes a source close to the Portugal camp:
It was just a precautionary measure that he rested for a couple of days after picking up a slight knock with Real Madrid.
He will be eased back in, as the squad step up their preparations, and he will be in the starting line-up. There is nothing more certain.
---End of Update---
Ronaldo has been struggling slightly with an injury to his left foot in recent weeks, but played in Real Madrid's demolition of Real Sociedad at the weekend.
Nevertheless, the Daily Mail reported on Tuesday that he missed training with the national team on Tuesday—a precautionary measure with Friday's first leg in Lisbon:
Cristiano Ronaldo missed training on Tuesday to hand Portugal a headache ahead of the first leg of their World Cup qualifier against Sweden on Friday.
The Real Madrid superstar is struggling with an injury to his left foot and spent the morning being assessed by the medical staff.
The match has been widely billed as Ronaldo against Zlatan Ibrahimovic, the Paris St. Germain striker who plays a similarly talismanic role for Sweden. Much has been made of how only one of them can be at next summer's World Cup.
The injury to Ronaldo is a concern, but it is unlikely it is a problem that will hinder him in one of the most important games in his country's recent history. With his position in the team assured, it is not imperative that he is available for every training session.
What is imperative is that he is able to play in both legs of the contest—so taking some time out at the beginning of preparations to assess his injury and how best to manage it seems eminently sensible.
Talking of things that are eminently sensible, here's how Zlatan Ibrahimovic has been preparing for the game against Portugal:
More than one way to build up towards a crucial international match, we guess.