Swansea defender Mike van der Hoorn says Manchester City got "top-team luck," against his side in their 3-2 FA Cup quarter final victory.
Manchester City's equaliser was a contentious penalty and their winning goal looked to be an offside.
VAR was not in use despite the Liberty Stadium being equipped for it.
"In this situation for us it (VAR) would have been a big help, because it cost us two goals," he said. "But it's not there, we can't do much about it."
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Substitute Sergio Aguero beat Swansea keeper Kristoffer Nordfeldt with a diving header for the winning goal, although replays showed the Argentina striker was marginally offside.
But the video assistant review system was not in use at the Liberty Stadium, despite having been used in City's third and fourth round ties at the Etihad. VAR is only being used this season in the FA Cup at Premier League grounds.
City, fighting back from 2-0 down with 21 minutes to play, had levelled in contentious circumstances too when Swansea defender Cameron Carter-Vickers was judged to have tripped replacement Raheem Sterling in the area.
"I'm sorry it was offside," Guardiola said afterwards of the winner.
"I don't understand why VAR is not used in this competition at this stage. Hopefully, next season this won't happen."
Van der Hoorn says it was unfair on the Swans, who did have VAR in operation in the FA Cup last season when they were a Premier League side.
"The penalty, I think it was very soft," he said.
"You could see he didn't touch the guy. For a foul I think you need to touch the opponent and he didn't do that.
"For the third one, yes, I think his foot was offside. It's top-team luck maybe, but they pressed us and forced everything to win the game."
When he was told that VAR was used in the other quarter-finals, van der Hoorn said: "Is it? That's a bit rude.
"I think you have to equal that. If you do it at one you should have them at all. For us, and even for City, it's a big game. We want to go to Wembley and that's a bit weird.
"Of course, you need a bit of luck. But we gave everything. We put bodies on the line and they were forcing us to make that tackle, to make that error."
Swansea's Bersant Celina, a former Manchester City player and scorer of Swansea's second goal, admits the manner of defeat is hard to take for the Championship side.
"I was right there and from what I hear Cameron touched the ball. I didn't think it was a penalty, I haven't looked at it, but personally I didn't think so," Celina explained.
"I thought Aguero was offside so it's very difficult to take. He looked offside at the time. I thought that at the time and I'm surprised nobody reacted. It's all hard to take."