Guardiola’s side were 2-0 winners at the Etihad Stadium thanks to goals from Omar Marmoush and Antoine Semenyo.
The Spaniard still wasn’t happy, however, slamming debutant referee Hallam for his decision to overrule VAR and not award City a penalty.
Hallam, who was refereeing his first Premier League game, was called to the pitch side monitor to take a better look at Yerson Mosquera but decided against giving the spot kick.
Speaking to reporters after the game, Guardiola didn’t hold back on his opinion of the decision, saying: "The referee made his debut, now everybody will know him.
It's the first time, I think, he'll go to the TV and disallow for a normal position of the arm. I'm pretty sure Howard Webb tomorrow is going to appear in the media to explain why it's not a penalty.
“What they've done against (Manchester) United - the first time they've done it, because the situation was a little bit of a doubt, right? That's why Jeremy (Doku) could not play (vs Bodo/Glimt), for the action from (Diogo) Dalot.
“But it's OK. I'm waiting tomorrow; don't wait until Wednesday, we have Champions League, we're busy. Howard Webb, come tomorrow, explain why it's not a penalty."