City fought back from 2-0 down to record a dramatic and controversial 3-2 victory in the quarter-final clash.
But the win will throw up further questions about VAR, which would have overruled Sergio Aguero’s last-gasp header for offside had it been in use.
The Liberty Stadium is equipped for VAR but because other Championship grounds are not, it was not operated for the sake of consistency.
There was also debate over City’s equaliser, which came from the penalty spot after Cameron Carter-Vickers was adjudged to have fouled Raheem Sterling.
Guardiola said: ‘If it is not a penalty, and it is offside like the people say, I’m sorry. They ask all the clubs about the VAR and all around Europe, the VAR is there and here is not.
‘I don’t like to lose games when the decisions are wrong but the referees don’t want to make wrong decisions, but they must be helped.
‘We deserved to win the game by far – but to win in that way, I’m sorry.’