Mauricio Pochettino says his Tottenham players did not "respect" his tactical plan during Wednesday's 2-2 draw with Olympiakos.
Spurs started the game in Greece in sluggish fashion but found themselves two goals to the good inside half an hour after a Harry Kane penalty and a fierce finish from Lucas Moura from 20 yards.
Olympiakos hit back just before half-time before tucking home their own spot kick after the break as Spurs let a commanding lead slip for the second time in just over a fortnight.
"I feel very disappointed," he told reporters. "To be honest, first half I wasn’t happy with our performance. From the beginning we had a plan and we didn't respect the plan. That was what disappointed me the most. I told the players at half-time.
"We conceded a lot of chances to Olympiakos and the way we conceded the first goal was so painful. We didn’t translate from Saturday that type of aggression these type of level of games demand. That is my biggest disappointment."
Spurs were two goals up away at rivals Arsenal earlier in September only two conceded seconds before half-time and then concede any equaliser.
Pochettino has questioned his players' preparations ahead of what was touted as a tough away trip which came after a thumping 4-0 win over Crystal Palace in the Premier League.
He added: "When we are not showing that intensity that the competition demands we struggle. We are not talking about quality. We're talking about being focused, concentrated, aggressive, anticipating the action.
"How many times did we anticipate today? How many times we were not proactive like we were against Palace.
"It's not about tactics, it's not about quality players, it's about the quality of preparing yourself to be ready to fight.
"At this type of level you need to match the opponent in terms of intensity, aggression, in excitement and motivation ... I feel disappointed for everyone."
