Leeds Crown Court heard Daniel Hook was caught on CCTV running into the man's store before launching a flying kick in to his face.
The man immediately fell to the ground and Hook can be seen bending over his victim before members of the public arrive and restrain him..
Hook's victim, who has type 2 diabetes, suffered two broken ribs and a cut above his eye and was left traumatised by the attack just after 3pm on December 27 2018.
Prosecutor, Robert Galley said Hook, 38, was restrained by a security guard and members of the public while his victim lay motionless on the floor for around three minutes.
Mr Galley said the man was treated in hospital overnight and had to visit hospitals on five further occasions.
Mr Galley said the attack has had a lasting impact on the victim, who wrote in a victim personal statement: "I find myself constantly stressed and worried."
The court heard the victim had never met Hook and doesn't know him.
Hook, of Autumn Terrace, Hyde Park, Leeds, admitted inflicting grievous bodily harm and failing to surrender to bail.
He has previous convictions for violent disorder, burglary, assault, possessing a bladed article and shop theft.
Hook appeared via video link from HMP Leeds, where he was already serving a 28-week jail sentence imposed on January 15 for breach of bail and 14 theft offences.
Shila Whitehead, mitigating, said: "He deeply regrets the way he behaved on that particular day. He is remorseful.
"He accepts he was using and abusing drugs at the time he committed this offence."
Judge Mustaq Khokar said: "You kicked him in the face, causing him to fall and whilst he was on the floor you are seen bent over him.
"Whether you threw punches or kicks, one doesn't know, but certainly something happens. It is most likely kicks in his body which caused fractures to two ribs."
Jailing Hook for two years and 14-days, Judge Khokar added: "This a very serious case, particularly when you do not advance any reason as to why you carried out the attack."
The latest sentence will run at the same time as the current jail sentence Hook is serving.