The attack was reported to have occurred in Foothills Park around 4 p.m. Saturday when a cougar attacked a hiker in his 50s, according to Palo Alto police Agent Dan Ryan.
Fish and Game investigators inspected the area and found nothing consistent with a mountain lion attack, said department spokesman Steve Martarano.
He said inspectors looked for evidence such as tracks or hairs, but could not find anything to substantiate the attack.
"We're not saying that a lion was not there," said Martarano. "We just haven't found any evidence of it."
A federal trapper who was brought in to capture the cougar has been released, according to Martarano.
Ryan said the victim who reported to be attacked by the mountain lion told investigators he was walking on a trail in the northwest corner of the park when the lion, estimated to be around 5 feet long, jumped on him from behind and caused him to fall about 15 feet down a hill where he collided with a tree.
He had injuries consistent with a fall but officials could not confirm he was attacked by a mountain lion, said Ryan, who added there was no evidence to say he was a lying. The man was in good condition today, he said.
Ryan said there was a second possible mountain lion sighting late Saturday afternoon in the Enid Pearson Arastradero Reserve, but the reporting party was about 50 yards away and was not certain it was cougar.