The trust then told Dr MN it wanted to investigate him over what he knew about Letby when she visited their hospital.
Dr MN said the trust breached its employment contract because it wanted to appoint someone other than its chief medical officer to oversee the investigation.
The judge ruled: “It is a term of Dr MN’s contract of employment that the case manager should be the medical director, in this case, the chief medical officer, for the matters that are the subject of the present investigation.”
Letby, 35, who has always maintained her innocence, lost two bids last year to challenge her convictions at the Court of Appeal.
The Criminal Cases Review Commission, which investigates potential miscarriages of justice, is reviewing her convictions.
Earlier this month, prosecutors revealed they were considering bringing further charges against her following the deaths and non-fatal collapses of babies at hospitals where she worked.