Lisbon - Cristiano Ronaldo travels to Luxembourg on Sunday with the objective of helping reigning champions Portugal qualify for Euro 2020 and the 100-goal mark for his country within his reach.

The former Real Madrid star is also eager to prove he is not a player in decline after his angry reaction to being substituted by Juventus coach Maurizio Sarri in the past two games.

The five-time Ballon d'Or winner, who turns 35 years in February, responded in typically defiant fashion with a hat-trick in Portugal's 6-0 win over Lithuania on Thursday.

It brought his tally to 98 goals in 163 games, to close in on Iranian striker Ali Daei's world record of 109 international goals scored between 1993 and 2006.

"I hope that tomorrow (Sunday) he'll score the most goals in his career," Portugal coach Fernando Santos told Saturday's pre-match press conference.

The symbolic century remains within arm's reach of the striker who despite the passing years has lost none of his lethal firepower.

Already the top Champions League scorer with 127 goals, ahead of his long-time rival Lionel Messi, Ronaldo this season broke the 700-goal mark in all competitions.

And with just two weeks to go before the Ballon d'Or trophy is awarded, the player from Madeira has yet another chance to hammer home his point on Sunday.

A win would help Portugal wrap up a spot at Euro 2020 and move on from the their 2-1 loss to Ukraine in Kiev last month. They hold a one-point advantage over Serbia in the battle for second behind Group B winners Ukraine.

Should they slip up unexpectedly, Ronaldo and co -- winners of the inaugural Nations League -- would have another shot via the play-offs.

On Sunday, Ronaldo will also be keen to prove once again to Sarri that he is physically fit.

The striker reacted furiously after he was substituted in his team's 2-1 Champions League win against Lokomotiv Moscow in Russia on November 6.

Four days later Ronaldo was again substituted in the Serie A match which the Turin giants won 1-0 against AC Milan.

Ronaldo was replaced after 55 minutes on the pretext that he had "a slight knee problem", with Paulo Dybala taking his place and scoring the winning goal.

The controversy swelled when the Italian media revealed that the Portuguese had aimed a few harsh words in Sarri's direction before returning directly to the locker room.

He left the stadium a few minutes before the final whistle.

Ronaldo broke his silence by taking to Instagram on Monday, stating: "Difficult game, important victory! #until the end."

His status could prevent him from being hit with a penalty or fine by Juve, but he should not escape a grilling by club vice-president Pavel Nedved, according to the Italian sports press.

Despite Ronaldo's poor performance last Sunday, his demonstration on Thursday against Lithuania led to a softening in tone in the Italian media, who had blasted his "lack of respect" for his team-mates.

"Here (in Portugal) CR7 does not go, he embraces (the coach) Fernando Santos and he remains on the bench. (...) It is clear that we do not waste time to demolish players, including champions," wrote Corriere dello Sport.

Relieved, the Portuguese press, heaped praise on Ronaldo after he scored his ninth international hat-trick "with no sign of injury".

Portugal will again rely on their talisman captain Sunday, and bank on his goals to do the talking.