The 37-year-old victim was in the Kelvingrove area of Glasgow's West End when his attacker approached at about 11am on Friday.
The victim was taken from Park Quadrant to hospital, where his condition was described as stable.
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Hide AdDetective Sergeant Stevie Smith appealed for a man seen walking a rottweiler dog in the area to contact police.
He added: "At the time of this attack, the area around Park Quadrant would have been busy with pedestrians and motorists and I would appeal to anyone who was in the area at or around the time of the incident to come forward."