Lord mayor Robert Doyle has told Melbourne City Council he is suffering from serious ill health, and the inquiry into sexual harassment allegations against him has been extended as a result.

Chief executive Ben Rimmer said on Friday that the council supported Cr Doyle's "focus on his health and we are very hopeful that he makes a full and speedy recovery".

Melbourne lord mayor Robert Doyle. Credit:Paul Jeffers

He said the council was "very conscious of the need to support all councillors and employees during this difficult time" and that the investigation would be completed as quickly as possible "in the interests of everyone involved".

Former councillor and Team Doyle member Tessa Sullivan resigned in December, alleging Cr Doyle harassed and indecently assaulted her. Councillor Cathy Oke also told the council's subsequent investigation that Cr Doyle had tried to kiss her, and clutched her thigh under a table in a separate incident.