Police investigating a robbery which has left a victim in a critical condition want to trace a man who answered his mobile phone.
Mr Hughes was found on a pavement in Northampton
Mark Hughes, 42, was found in a Northampton street with serious head and facial injuries.
Police said he left his home in Maidencastle late on Sunday to visit his girlfriend but did not arrive.
He was found in Wellingborough Road early on Monday. His mobile phone and wallet had been stolen.
Police have revealed that soon after Mr Hughes was reported missing, his phone was answered by a man who told the caller he had found it.
The man then rang off before giving any further details.
Det Ch Insp Jan Terblans appealed for the man to come forward and help the investigation.
"This man could clearly be a very important witness in this investigation and we need him to come forward and contact Northamptonshire Police as soon as he can," she said.
Mr Hughes remains in a critical but stable condition at Northampton General Hospital where he is being treated for a head injury.
Police are still requesting information from anyone who saw Mr Hughes late on Sunday.
"We have had a very positive response to our appeals for help but I still need to hear from anyone who saw Mark or found his property, and especially the man who answered his phone," Det Ch Insp Terblans added.