It is understood that Chelsea's former team doctor is seeking a claim for constructive dismissal.
Lawyers for Dr Eva Carneiro are believed to have sent legal papers to the club.
It could lead to an employment tribunal, unless an out-of-court settlement can be agreed.
Dr Carneiro was dropped from first-team duties after being criticised by manager Jose Mourinho for attending to player, Eden Hazard, in the closing stages of a game in August.
The Football Medical Association were among those to back Carneiro and club physio Jon Fearn over the issue.
She has since left the club in the wake of the controversy.
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