Mauricio Pochettino insisted the packed festive schedule has left his Tottenham players lacking "energy" after seeing his side slip to a 3-1 defeat to Wolves.
Spurs have played three games in the last seven days, and were expected to get the better of Wolves at Wembley having come into the match having won their last five league games in a row.
Harry Kane's early strike put Spurs a goal to the good as they looked to keep pace with leaders Liverpool, but three late Wolves strikes turned the match on its head to stun Spurs, who Pochettino feels just ran out of steam.
"That is football," Pochettino told Sky Sports. "Sometimes it is very difficult to explain. In the first half we dominated, had lots of chances and controlled the game.
"In the second half we started to feel the effort from [the amount of] fixtures and everything. We needed more energy.
"You need to play not only with quality but with energy and it was difficult to find energy. We miss that fresh energy that we needed to find the second goal. We were a little comfortable because they played so deep. When you don't kill the game, in a period when it is so tough to play every three days, it is tough."
Wolves came into the encounter looking for a first win in three against in-form Spurs, and managed to continue their fine form against "big six" sides, with Pochettino adamant Wolves' victory should not be such a surprise.
"The Premier League is so tough to play," Pochettino added. "Any team can beat you. We drop a little bit in our focus and our concentration in the last 20 minutes.
"This period is so tough. It is not easy for the player to compete at their top level. I need to back them and we go again for the next game."