Ruben Dias pleaded with the Portuguese media to promote unity rather than trying to create a divide following criticism of Cristiano Ronaldo.
Fernando Santos' Portugal side will face Switzerland in the last 16 of the World Cup on Tuesday after winning Group H despite a shock defeat to South Korea on matchday three.
Ronaldo endured a particularly difficult day against the Taeguk Warriors.
He failed to hit the target with either of his two shots and was caught offside three times, with a couple of those situations raising questions of his concentration.
The 37-year-old was withdrawn in the second half and simultaneously had a disagreement with South Korea forward Cho Gue-sung.
Since then, a poll on the website of Portuguese newspaper A Bola suggests 70 per cent of supporters want Ronaldo to be dropped, and defender Dias had a defiant response.
"I actually think you shouldn't ask Ruben Dias that, but you should ask that to Cristiano Ronaldo," the defender told reporters.
"I'd like to take this moment to say, in this tournament the press is supporting us and Ronaldo, so I'd like to make an appeal to the press; as we progress, instead of creating a divide, create unity, then who knows maybe we'll have good strength and positive energy for all involved."
If Ronaldo was to be dropped, Rafael Leao would be among the favourites to step in.
The Milan forward came on as a substitute in all three of Portugal's group games, but Santos appears to think he still requires some adaptation work.
"He has a huge potential, and I think he will have a promising career," Santos added.
"But of course he faces the difficulties of any player who has a place in a club like his, where he plays more on the left and playing for the club he has more freedom.
"But at national team level, he needs to adapt to the others, to players who excel for their clubs but have a different [role] at the national team."