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Wasn't Diarra in a situation where he'd been sacked by Lokomotiv Moscow, then was unable to take up a contract offer elsewhere because Lokomotiv Moscow refused to release him from the remaining two years of his contract, even though they'd terminated it?
LM then successfully persuaded FIFA to suspend him for 15 months and fine him €10 million. The court case arose out of that disciplinary case brought by FIFA.
Just like "normal" employment then, notice period aside. As you say, really interesting!