A man was found with a collapsed lung, broken ribs, and cuts and bruises to his face on Skerton Bridge in Lancaster.
It is thought the 39-year-old had walked from Lancaster city centre and was seen just before 7.30pm on Thursday July 31 walking close to Skerton bridge, before he was found collapsed in the road by police.
Police have not said whether or not the man had been attacked.
The man, from Skerton, was treated at the Royal Preston Hospital for broken ribs, a back injury and a collapsed lung.
DS Simon Ball of Lancaster and Morecambe CID, said: “We are keen to speak to anyone who may have seen this man walking from Lancaster city centre or who may have been driving close to Skerton Bridge at the time.
“Anyone with information should contact police on 101 quoting log number LC-20140731-1220 or Crimestoppers anonymously on 0800 555 111.”
The man is described as white, 6ft tall with short dark hair and of a stocky build. He was wearing a black t-shirt and black stonewashed jeans.