Haaland, who joined from Borussia Dortmund this season, has scored 45 goals in all competitions for City -- a single-season record for any Premier League player.
There had been concerns over Haaland's fitness ahead of his transfer after he missed 16 games due to injury for Dortmund last term, but the Norway international has missed only four for City this campaign.
"I don't know what he's done in Dortmund but we take care of him 24 hours," Guardiola told reporters on Friday. "We have incredible doctors and physiotherapists, they are behind him every second of the day.
"It's difficult to understand why you spend a lot of money (on a player) and then leave them – I don't know what the other clubs do."
Guardiola said keeping Haaland fit was important amid a hectic schedule, adding that they are extra careful owing to his 6 feet 5 inches stature.
"Today with this demanding schedule of games every three or four days we have to take care of them," Guardiola said.
"It's so demanding, with nutrition, rest, sleep, food... We know we have to watch him because he's so big. The physios take care of him; he is massaged – his back, shoulders, tendons, everything.
"He works so much time inside the training centre – much more than on the pitch. Today in modern football, players train more behind the scenes than on the pitch."
City are second in the league, six points behind leaders Arsenal with a game in hand. They are also in the hunt for the Champions League and FA Cup.
