Hazard was completely dropped from the squad by manager Jose Mourinho.
The Daily Mail says it is understood Hazard, who played in the 2-0 defeat to Newcastle on Saturday, travelled to Lille on Sunday morning for a reunion with his former team-mates and to watch his ex-club take on Monaco later that evening.
Hazard was due to board an early Eurostar train back to London on Monday morning in time to report for training at Chelsea' Cobham HQ, but did not make it.
And Mourinho confirmed: "He missed training on Monday. He forgot the time? That's the end of story. He's a kid.
"Kids make mistakes and fathers have to be clever in the way they educate their sons. He didn't play. He wanted to play.
"He was sad because he didn't play. We won without him. On Saturday, he is back. So, end of story."
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