Portugal head coach Fernando Santos says Cristiano Ronaldo is an inspiration to the younger players in his squad.

The Real Madrid forward is set to make his first appearance for his country since the Euro 2016 final when they face Andorra in World Cup qualifying on Friday.

Ronaldo, who was forced off in the first half of that 1-0 win over France with a knee injury, returned to the dugout to motivate his team-mates as they went on to claim the trophy thanks to Eder's extra-time strike.

Santos, however, says his captain's successes at club level - which include three Champions League titles - are a true source of motivation for the rising stars at his disposal.

"When you have the best player in the world, what do you think will happen? Cristiano is Cristiano," he said. 

"Of course, he always wants to be present in the national team and has a lot of value. It's not only the quality he has, but he means a lot to the younger ones.

"He is a player who has many titles, and always want to win more and more, and this is very important in this team, which has many players who are taking their first steps.

"Many of them have won a very important trophy, but do not have so many titles in their careers. And you know how important a player is who has titles, because it gives them strength. And as I said, the presence of Cristiano has a lot of value for the team."

Portugal suffered a 2-0 defeat to Switzerland in their opening qualifying match, but Santos has no concerns that the European champions will not be involved at Russia 2018.

"I am sure that Portugal will be at the world championship," he said. "It's a team of great quality. They know very well what they have to do and I have great confidence in them.

"The World Cup is something that I've never had with Portugal. It's the first time. It's natural that the players have an ambitious outlook, it is natural that they want to be in this championship."