Maguire’s poor form has played a major role in United’s struggles this season.
It had been reported the world’s most expensive defender felt undermined by Ronaldo’s influence, but Maguire denied that claim and Rangnick insisted his status as captain has never been questioned.
“This is absolutely nonsense. I have never spoken with any player about a possible change of captaincy,” said Rangnick at his pre-match press conference ahead of Sunday’s trip to Leeds.
“This has never been an issue for me, it’s me who decides who is captain and therefore there is no reason for me to speak about that with any other person.
“Harry Maguire is our captain and he will stay our captain until the end of the season.”
Maguire was made skipper by then manager Ole Gunnar Solskjaer in January 2020, just five months after joining the club from Leicester for £80 million ($109 million).
“I’ve seen a lot of reports about this club that aren’t true and this is another,” Maguire posted on Twitter.
“Not going to start posting about everything that is written but I needed to make this one clear. We’re united and focused on Sunday.”
United forward Marcus Rashford also dismissed talk of a dressing room divide involving Ronaldo earlier this week.
A 2-0 win against Brighton on Tuesday lifted United back into fourth place in the Premier League, which would be good enough to qualify for next season’s Champions League.
But Arsenal, Tottenham and Wolves have games in hand which could see them move above the Red Devils.
Ronaldo was vocal in his support of Maguire after returning for his second spell at United in August, but his backing is reported to have waned as the season has gone on.
The two players are believed to have spoken to Rangnick about the possibility of Ronaldo taking the captain’s armband so Maguire can focus on improving his erratic form.
But the England centre-back is understood to be concerned about the prospect of losing the captaincy permanently.
While Maguire has made a number of high-profile mistakes this season, Ronaldo has also suffered notable dips in form.
There have been several reports Ronaldo is unimpressed by Rangnick’s management style, with the striker stomping off the pitch and exchanging words with the German after being substituted in a victory at Brentford in January.
The 37-year-old went six games without a goal before finally getting back on the scoresheet against Brighton in midweek.
That victory stopped a dismal run of three successive games in which United had blown a first-half lead.
Rangnick said earlier this week United’s self-belief had been dented by their recent habit of throwing away leads, admitting that finishing fourth in the Premier League was the best they could now hope for.