The original draw saw Manchester City selected to face Villarreal, but that was declared void by UEFA after it became apparent several errors had taken place.
A mix-up meant Villarreal were originally drawn against Manchester United, but the two sides were not permitted to face each other having qualified from the same group.
A second mistake then saw United omitted from the pot of potential opponents for Atletico Madrid, of which Liverpool were included in despite the fact that United were eligible to face the Spanish outfit and Liverpool, who played them in the group stage, were not.
A statement from UEFA said the errors were due to technical problems with the software that instructs officials which teams are eligible to face one another.
“It’s going to happen again, so I think that’s fair,” he explained at his press conference prior to City’s Premier League game against Leeds United.
“It was a mistake. These kinds of things sometimes happen, especially for the players and managers, so sometimes UEFA [can] too.
“We are going to wait. Like I always said, I am more than satisfied to be a part of that.
“I think it is fair. It is a mistake, so you have to repeat so there are no suspicions. All the opponents are tough.
“People say one is better than the other but all of them at this stage are difficult.”
The 26-year-old has started each of City’s last three games since returning from injury and the manager has been impressed with his contribution.
Grealish has scored twice in 19 appearances since his summer move from Aston Villa and, when asked about the midfielder’s attacking output, Guardiola said there is no pressure on him to add more goals to his game.
“He doesn’t have to score,” he added.
“He has to do exactly what he is doing, no more than that. The rest will come in time.
“He has chances to score two or three goals every game and one day he is going to do it.
“He could have scored a hat-trick against Watford without a problem. Last game [he could have scored] one or two goals again. It’s going to happen. The way he is playing is good.
“It was a difficult game [against Wolves], but he was patient and his decision making was good. He made a contribution.
“He has been so important for us so far this season. He has played a lot of minutes.
“The reason why we finished first in the Champions League group stage and are where we are in the Premier League is because of his contribution.
“He is going to improve, of course. During the season we don’t have 38 games where all the players are performing really well.
“Never in my career have I found a player in one season from the beginning to the end to stay on top.
“Sometimes there are high and lows. What we want is the high moments to continue as much as possible.”