Ronaldo went off in the first half of the Euro 2020 qualifier with an apparent hamstring injury. The match ended 1-1.
"I'll know more in 24 or 48 hours," he told reporters.
"It happens, it's football. If you go out in the rain you get wet... I'm calm, I'll be back in one or two weeks."
His club Juventus later said in a statement that the 34-year-old had undergone exams in Portugal which showed "an apparent minor injury to his right thigh flexors."
"His condition will be monitored and will be subjected to new investigations to define the resumption of competitive activity," it said.
A long absence would be a blow to Juve, who signed Ronaldo last year to boost their chances of winning the Champions League. Juventus travel to face Ajax Amsterdam in their quarter-final first leg on April 10 with the return six days later.
Both Ronaldo and Portugal coach Fernando Santos said the referee had apologised to them for not awarding them a penalty for handball in the second half.
The referee initially gave the spot kick but then changed his mind. Video assistant referees (VAR) are not used in the Euro 2020 qualifiers.
"It was very clear, the referee should have given it," said Ronaldo. "The linesman was 40 metres away so it seems a bit strange."
Santos said: "We saw the incident in the dressing room afterwards and neither we nor he had any doubt -- it was a penalty... He apologised."
(Writing by Brian Homewood; Editing by Peter Rutherford and Christian Radnedge)
