The man was punched by four teenagers as he walked in The Quarry, in Shrewsbury.
Police said the attack took place between 8pm and 8.30pm on Friday, April 2.
A spokesman for the police said: "The victim was hit over the head and punched by the offenders causing him to suffer serious head and back injuries."
Anyone with information is urged to call 101 quoting reference 689i of April 3 or alternatively report it online through the 'Tell Us About' section of West Mercia Police force's website.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org