Hikers discovered the body, which had no signs of identification, near the rural hamlet of El Puerto, in Asturias on Sunday evening.
The extremely thin appearance of the body has led local police to hypothesize that he may have been held captive before his death, although they are not ruling out other lines of enquiry at this stage, reported Spanish newspaper, La Opinión de Murcia.
The two hikers, from León, alerted authorities to the gruesome find just after 6pm on Sunday January 11th. They found the man, who was middle aged – between 45 and 60 years old – close to a trail that runs parallel to the motorway, around one kilometre (0.62 miles) from the hamlet of El Puerto.
The surrounding area is popular with tourists who come to watch chamois, which are native to the area.
The body was moved to a regional forensic institute where an autopsy was carried out, the results of which have yet to be released.
A blanket was found a few metres below the body, which could have been to transport it. Investigators believe the crime was not committed at the scene.
The state of decomposition of the body suggests the death was not recent. Investigators believe it was dumped in the area, at most, about a week ago.
Investigators have, so far, not been able to determine the number of people involved in any possible crime; the man weighed so little – only 50kg (110 pounds) – that he could have been carried by one person.
The missing foot was presumably eaten by animals, according to the La Opinión de Murcia.