Lampard becomes a free agent at the end of the month.
Mourinho said: "You can't imagine how difficult it was. I think only Frank knows that, but at the same time I can feel some happiness about the process because, for sure, he comes back to Chelsea.
"He can be a coach, he can start at the academy, he can start being my assistant at the same time because he is doing his coaching badges, or he can start in a different role."
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