Tottenham manager Mauricio Pochettino accused his players of not respecting the plan after they squandered a two-goal lead to draw 2-2 away to Olympiakos in their Champions League opener on Wednesday.
Tottenham then conceded a penalty which Mathieu Valbuena converted in the 54th minute.
With Bayern Munich up next it was a great opportunity for Tottenham, who made a surprise run to last season's final, to put themselves in a strong position in Group B.
It is the second time Tottenham have allowed a two-goal lead to slip this season after also drawing 2-2 at Arsenal in the Premier League.
"I feel very disappointed. To be honest, first half I wasn't happy with our performance," Pochettino said.
"From the beginning we had a plan. We didn't respect the plan. I told the players at half-time. We scored two goals but if you only analyse the performance it wasn't great.
"We conceded a lot of chances to them and the first goal was painful. We didn't show the aggression these games demand."
It was a strange display by Tottenham who appeared to be playing in second gear at times and failed to show the ruthless streak needed to see out games in Europe.
Since scoring a last-gasp winner at Fulham in the Premier League in January, Tottenham have managed just only two victories on the road -- both in the Champions League against Borussia Dortmund and Ajax.
No team has conceded more Champions League goals (21) than Tottenham since the start of last season.
"At this level you need to match your opponents. That is the first demand," Pochettino said. "It's not about tactics or quality players but the level of fight. You need to match the opponent in aggressivity, excitement, motivation."
French midfielder Valbuena praised his side's response after finding themselves in trouble so early.
"It was hard seeing Tottenham taking a 2-0 lead, when we had wasted several opportunities of our own," he said. "We didn't despair though and we had a great performance tonight.
"We are proud of ourselves and our fans who helped us a lot. We were two goals down and everyone thought we would give up. But that wasn't the case. We continued and showed excellent mentality and strength of character."