Mourinho says referee Cuneyt Cakir emphasised in a meeting on Wednesday morning that the second halves of Chelsea's victory over the Portuguese side and Dynamo Kyiv's clash with Maccabi Tel Aviv must kick off at the same time.
If either team is late arriving back on the pitch the manager is punishable, so the 52-year-old left his players earlier than normal to make sure he was not culpable for any delays.
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"It's simple," Mourinho told reporters. "The rules in Uefa are that, if the team are late at half-time, the manager is suspended for the next match. It's his responsibility.
"Today the referee was very clear in the meeting in the morning that the Chelsea-Porto and Dynamo-Maccabi matches should start at the same time, so I went there to show that, if somebody is late, it's not my fault."