The 19-year-old is being questioned by West Midlands Police.
The victim was left with a bloodied nose and black eye after a woman punched him in the face before shoving him to the ground in the daylight attack in Coventry.
West Midlands Police have appealed to social media users after a video of the attack in the city's Trinity Street, near Millennium Place, was uploaded. The footage, captured by a passer-by on a camera phone, provoked widespread anger among internet users.
Police had earlier issued a series of still images showing the assault in the hope that witnesses, or members of the public with information about the incident, would contact the investigation team.
Coventry Police Chief Superintendent Andy Nicholson said yesterday: "This is a despicable, violent attack on an elderly man in broad daylight. A video showing the assault is gathering momentum on social media and quite rightly the woman's actions are being condemned by everyone who has viewed it.
"Detectives in Coventry are fast-tracking this investigation. We're doing everything we can to arrest the man's attacker as soon as possible.
"I'd encourage the woman to make contact with West Midlands Police as it's only a matter of time before we catch up with her."
The attack, which appears unprovoked, happened at around 8.30pm on August 10 near Sainsbury's in Coventry's Trinity Street.
Names of potential suspects have been circulating on social media websites.