City were without the Norway striker for the first time this season due to an ankle injury picked up against his former club Borussia Dortmund in midweek and they missed his predatory instincts.
In the end they needed a stunning free-kick from Kevin De Bruyne to get past a dogged Leicester side who were set up to contain the champions.
Haaland has scored 22 goals this term but one of the rare times he did not was against Bournemouth who set up in the same way as the Foxes.
Guardiola said: "Nobody knows what would have happened with Erling Haaland.
"Erling played against Bournemouth in the shape like Leicester played with five at the back, four in the middle and Vardy dropping and he struggled. It is difficult.
"The best thing I can say, in this type of game, is don't get frustrated when you attack. If you concede a goal it is almost a hill to climb that would not be possible. So don't get frustrated and concede free-kicks and corners.
"We won but maybe one corner, one set-piece situation and you can draw the game.
"It is a massive victory because Leicester away is always tough. We arrived in the best moment for them and it was good to go to the top of the league."
Guardiola says Haaland will definitely miss the midweek Champions League game with Sevilla and will be assessed ahead of the Fulham game next week.
"I am pretty sure against Sevilla, no. First because we have qualified. Against Fulham we will see. We have seven days until then so we will see," he added.
De Bruyne showcased his talent with his brilliant 25-yard free-kick four minutes after the restart, but the Belgium international has not been without recent criticism from Guardiola, who said he wanted more from him.
The Spaniard said he would not be doing his job properly if he did not give his midfielder some constructive criticism.
"Kevin can do free-kicks, we know it," he said. "But he is a player who needs his dynamic. He has the quality when he moves, he needs movement and today he was back.
"We need him. It is not about he can't do it. Over the past seven years we have done everything together, except the Champions League.
"I know him quite well. Nothing is going to change my opinion of him or what he has done for this club or for me personally.
"But I have the duty in my job to say I want more. In the game against Brighton he scored a fantastic goal, but we need more. He can do that blind, naturally. We need both and today was the case."
Leicester manager Brendan Rodgers conceded he had to change to a more defensive shape to contain City, but still could have come away with a point.
Ederson had to produce a stunning save to deny Youri Tielemans' brilliant first-time volley from a corner.
"I think the players deserve a lot of credit, they carried out the game plan we wanted in terms of styaing in the game," said Rodgers.
"It's not the way we usually play but we have to respect arguably the best team in the world. We defended well in those moments.
"They had lots of the ball but our players stood up very strong to that and didn't give away too many opportunities.
"By the end we could have had something from the game. We were unfortunate not to get something."