Tottenham defender Matt Doherty admitted frustration after their 1-1 draw with Sporting CP.
VAR denied Spurs a late winner, so leaving their Champions League round 16 chances wide open.
Doherty said: “I think you can see from the celebrations we thought we won it. I don’t really know what happened at the end.
“I thought because it went backwards and hit a defender it was a different phase of play. I’ll have to look at the rule book. A few of us don’t have a clue what happened.
“If we’re being honest we didn’t play that well. They nullified us in the first half and deserved to be ahead.
“We’re top of the group. It’s not how we wanted the night to go but it’s still in our hands.
“I wish we knew [why they can’t play well for a whole game]. We’re analysing games and training sessions, watching a lot of videos to find out how we can perform for 90 minutes and play like we can play.
“We have a few days to look back and see what went wrong before we play on Saturday.
“I think it’s clear to see we want to play like we did in the second half for 90 minutes. We know we’re capable of doing it but it’s what we’re struggling to do.”