Cancer specialist Anthony Owen, 68, was found with head injuries in the road leading to his £700,000 thatch-roofed detached home in Cheshire in earlier this year.
Devout Roman Catholic Dr Owen apparently fell to the ground just yards from his Honda Civic car in Hale, near Liverpool, at around 10.20pm on Sunday 11th March.
He fought for his life at Walton Neurological Centre in Liverpool for six days but never regained consciousness and died on Saturday 17th March.
Following Dr Owen's death three youths were arrested by Cheshire police and 16-year-old was later charged with his manslaughter.
The youth, who cannot be named for legal reasons, has been due to appear before Chester Crown Court to enter a plea to the charge.
But the Crown Prosecution Service said the case had been dropped at a procedural hearing before Recorder of Liverpool Judge Clement Goldstone QC at Liverpool Crown Court on 20th July.
Rachael Barber, Senior Crown Prosecutor, CPS Mersey-Cheshire, said: "After very careful consideration of all the evidence in this case, including new evidence which has recently been presented, I have decided not to continue the case against a seventeen-year-old youth in connection with the death of Anthony Owen.
"The youth was originally charged with manslaughter on the basis that there was a reasonable suspicion he had committed the offence and there were grounds for believing that the continuing investigation would provide further evidence to support the prosecution.
"Since then new evidence has been presented, including the final pathologist's report which indicates that the injuries to the victim were consistent with the victim suffering one blow to the face.
"The pathologist's report provides supporting evidence for the defendant's version of events: that he was acting in self defence.
"This expected further evidence has not provided us with a stronger case to meet the test of sufficient evidence for a realistic prospect of conviction.
"Crown Prosecutors are required to keep all cases under continuous review. Where the realistic prospect of conviction test is not met a case must not go ahead no matter how serious it is.
"After careful consideration of all the evidence including the pathology report and the fact that there are no independent witnesses, we have decided that we would not be able in court to rebut the defendant's claim that he was acting in self-defence.
"In addition, we took into account that he had come forward voluntarily to give his account and that he has no previous convictions.
"We have therefore concluded there is no realistic prospect of conviction in this case and have formally offered no evidence against the defendant.
"We understand that this decision is difficult for Mr Owen's family, friends and members of the community to understand. We have met with Mr Owen's family to explain our decision to them in person.
"Two other youths who were at the scene at the time were released without charge as there was no evidence that implicated either of them."
Three youths aged 14, 16, and 17 had been formally arrested on 20th March after police appealed for information about three youths seen leaving the scene on BMX bikes at around the time Mr Owen was found.
