George Andrews, 69, claims doctors at Glasgow Royal Infirmary misdiagnosed his partner Jean Graham, 77, with Norovirus, the winter vomiting bug.
Ms Graham was taken by ambulance to the hospital's accident and emergency department from their home in Dennistoun, Glasgow, on two consecutive weekend nights in January last year. On both occasions doctors sent her home after assessing her as suffering from a bug. A day later, she was dead.
NHS Greater Glasgow and Clyde apologised to Mr Andrews but he has instructed lawyers with a view to pursuing a claim for medical negligence.
Mr Andrews said: "We put our trust in the NHS and they let us down. No-one should go through what happened to Jean. I want justice for Jean"
His lawyer Cameron Fyfe said: "There may have been negligence on the part of the hospital in discharging Jean on the Sunday when it seemed clear to George that she was seriously ill."
His claim comes amid calls for a full-scale review of doctors and nurses' numbers in Scottish hospitals on Saturdays and Sundays.
A spokeswoman for NHS Greater Glasgow and Clyde said: "We'd like to once again express our sincere condolences to Mr Andrews for his loss. We fully accept that there were lessons to be learned, in particular, the need to improve communication between clinicians in relation to the issue of the patient's previous presentations."