The Norwegian has started every Manchester City match so far this season and also went deep into the World Cup with Norway, who reached the quarter-finals, leaving Maresca mindful of his workload heading into Tuesday's trip to Estádio do Dragão.
"It's normal for these players to start showing signs of fatigue. So it makes sense to give them a rest, whether that's a match or a week," Maresca said, explaining his thinking around squad management at this stage of the season.
"When you see them tired, the risk of injury increases, and we need players at 100 per cent."
Should Haaland be left out at Porto, Phil Foden or Rayan Cherki could be deployed in a false nine role in his absence.
Maresca also reflected on Haaland's development away from the pitch, crediting the birth of his son in 2024 with a shift in the striker's outlook.
"He's a man now. He's a father. When he arrived here, he wasn't a father yet, and now he is, and his life has completely changed because his priority has become his son," the Italian head coach said.
Manchester City's squad management is further complicated by the uncertainty surrounding Jérémy Doku's fitness, with the Belgian winger still working his way back from a calf injury sustained in last month's Community Shield defeat to Arsenal, while Nico O'Reilly is available for selection after recovering from a back problem that forced him out of Saturday's win over Coventry.
Maresca must balance those competing considerations against the demands of a Champions League campaign that begins in Portugal before quickly turning to Sunday's Manchester derby against Michael Carrick's United at Old Trafford, his first meeting with City's local rivals since taking charge.
Haaland has scored freely since the start of the season, continuing a run of form that made him the Premier League's top scorer last term, and Maresca has stressed the importance of managing his squad's physical output given the compressed nature of the modern calendar.
Norway's run to the World Cup quarter-finals this summer means several of City's international players, Haaland included, arrived back for pre-season with a shorter break than usual, a factor Maresca has cited when explaining his approach to squad rotation this season.