The man was rescued by firefighters from the ground floor flat at Park Court, Park Street, Kidderminster, Worcestershire, on Wednesday evening.
He was critical but stable on Thursday after being taken to hospital suffering from severe burns and smoke inhalation.
There were early indications the fire had been started deliberately, West Mercia Police said.
The fire was confined to the flat, which was gutted, although there was some smoke damage to a property above.
Emergency services were alerted by a neighbour who got out by himself.
Det Con Philip Christie, of Kidderminster CID, said: "We need to establish exactly what happened and want to hear from anyone who witnessed the blaze or was passing by and heard or saw any suspicious activity around the flats."
The injured man was rescued at about 2030 BST.
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