Cristiano Ronaldo is unconcerned by the injury he sustained in Portugal's 1-1 draw with Serbia and believes he will be able to return within two weeks.

Ronaldo went off 31 minutes into Monday's Euro 2020 qualifier in Lisbon after appearing to sustain a muscle problem while chasing after the ball.

But the 34-year-old insisted the issue is not serious and he hopes to be fit in time for the first leg of Juventus' Champions League quarter-final against Ajax on April 10.

Juve are scheduled to travel to Cagliari between home Serie A clashes against Empoli and AC Milan before heading to Amsterdam.

"I'm not worried about this, I know my body," Ronaldo told reporters. "I know I should be back in a week or two."

Portugal fell behind early on to a Dusan Tadic penalty, but Danilo Pereira's thunderous effort drew the hosts level just before half-time.

The reigning European champions looked to have been handed a lifeline in the second half when Antonio Rukavina handled in the area, only for referee Szymon Marciniak to controversially change his initial decision to award a spot-kick after consulting with his assistant.

Ronaldo slammed the referee for going back on his call, saying: "It was annoying, because the team did everything. We created opportunities, played better – Serbia did not have great opportunities.

"In my opinion the referee should have given penalty. The assistant is 40 metres away and makes the decision for the referee? It seems strange to me."

Coach Fernando Santos, meanwhile, revealed Marciniak had apologised for his mistake.

"He invited me into his room to take a look at the incident. We saw it and we had no doubts, neither he nor I, and then he apologised," Santos said.

"But the excuse does not help me. No one who is 40 metres away can say it isn't [a penalty], especially when the referee sees it. What will I do with the excuse?

"The assistant was there and I said that it was his fault."

Portugal are not in qualifying action again until September and sit third in Group B with two points from their opening two fixtures, which were both played at home.