Cristiano Ronaldo will not be stripped of the Portugal captaincy after his "moment of great frustration" in the closing stages of Saturday's controversial draw with Serbia, head coach Fernando Santos has insisted.

Ronaldo was convinced his last-gasp effort crossed the line, but the officials disagreed as Serbia rallied from two goals down to secure a 2-2 draw in World Cup qualifying.

Stefan Mitrovic made back-to-back goal-line clearances to thwart Portugal in stoppage time, though Ronaldo was adamant his effort crossed the line in Belgrade, where there was no VAR in place to review the decision.

Ronaldo was booked for his protestations before he angrily threw his captain's armband on the floor and walked off the field with just seconds remaining.

Santos revealed after the game that "embarrassed" referee Danny Makkelie had apologised upon reviewing footage of the incident. 

While Santos accepts Ronaldo should not have behaved the way he did, the Portugal boss has no intention of taking the captain's armband away from his talisman ahead of Tuesday's Group A clash with Luxembourg. 

"He will keep the armband," Santos told a media conference. "If he had offended the coach, his colleagues or the federation, then yes, we would have to think. Nothing like that happened. 

"What happened was a moment of great frustration that could have happened to me. Frustration of someone who always wants to win, who gives everything for the national team. It happened to him, it could have been someone else. 

"He was the first to recognise that he should not have done it. He will be captain for sure."

Midfielder Ruben Neves spoke alongside Santos on Monday and hailed Ronaldo as an "exemplary captain". 

"He did not apologise and he does not have to," the Wolves man said. "He is an exemplary captain for everyone. 

"We all felt the frustration he felt at that moment; it was a difficult moment for everyone. We know Ronaldo very well and we know what he can give us every day."

Portugal are level with Serbia on four points atop Group A, one point ahead of Luxembourg after their stunning win over the Republic of Ireland.