Jonathan Alan Smith, known as Johnny, was discovered by police at a flat on Middleton Road at about 16:10 BST on Wednesday following concerns about his welfare.
A post-mortem examination revealed the 44-year-old died from a single stab wound to the chest.
Police said they are unsure at this stage if anyone else was involved.
Det Insp Lewis Hughes, of Greater Manchester Police, said: "We were initially called by a concerned neighbour who said they had not seen Johnny for a few days and were worried.
"At this moment in time, we do not know what has happened to him or whether a third party was involved in his death."
"Johnny was last seen in Chadderton town centre on 11 May and I would ask anyone who may have been in contact with him either that day or up until his death, to contact us."
Police are investigating the "unexplained" death of man found stabbed in the chest in Oldham.