The Italian manager was filmed storming off the pitch in Baku the night before the Blues' clash with Arsenal, throwing his cap on the ground and kicking it away in anger.
The incident provoked much speculation, with an altercation between David Luiz and Gonzalo Higuain being suggested in some quarters as a possible reason.
However, Fabregas said that the coach’s inability to work on set-piece routines during an open session in front of the media was to blame.
"I guarantee you, this is the truth,” the Spaniard told BT Sport.
“I know him. He’s very superstitious. He loves to do set-piece tactics the last thing the day before the game. And they didn’t allow him to do it because it was an open session.
“The superstition is too much for him, he has to do it that way.”
Chelsea went on to win the game 4-1 , with all the goals coming in the second half.
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