Lisbon, Jun 7 (IANS): Portugal national football team coach Fernando Santos has said he is still uncertain about the line-up for his side's FIFA World Cup opener against Spain.

"I have many doubts," Santos told reporters at a press conference, reports Efe.

"I have 23 players, all of whom I fully trust. The match against Spain is in one week. We'll see what happens during training," he said, adding that he will make his final decision "at the proper time."

Despite the uncertainty, all-time scoring leader Cristiano Ronaldo - who missed the last two games and arrived at the camp just two days ago - is sure to captain the team against Algeria in a friendly match on Thursday.

"The world's best player will always be very important and a great influence," Santos said. "Wherever he is, he will always be very important for his team."

Santos also said that he has "great respect" for the Algerians, adding that they have players of great technical quality.

Portugal will face off against Algeria in their last friendly before the upcoming World Cup in Russia, following the 2-2 and 0-0 ties against Tunisia and Belgium, respectively.

The team will play their first World Cup match against Spain on June 15, later going up against the other members of their group: Iran and Morocco.