Maguire was caught out defensively in United’s recent 1-1 draw with Burnley and again on the weekend in the 1-1 draw with Southampton.
United fans have called for Maguire to be demoted from the starting line-up, or even be dropped as captain.
But Rangnick moved to downplay those calls ahead of United’s midweek clash with Brighton and Hove Albion.
“I think after he came back after his injury he did extremely well, with a very good performance against West Ham,” Rangnick told reporters.
“In the last two games he had some weaker moments, both against Southampton and when we conceded the goal against Burnley.
“He is our captain and I don’t see any reason to change that, but he is a player who has to develop and get better, like all the other players.
“The way we play is new. In the English national team he is used to playing in a back three, here he’s in a back four but not as proactive. It will take some time for him to get used to it.”
United are currently fifth and unbeaten in the league in their past five games but have struggled to mount a legitimate top-four challenge.
The Red Devils have kept only five clean sheets in 24 games this Premier League season and conceded 32 goals too.