A cyclist smashed a bus window and attacked the driver on one of the city's busiest roads.
The bus driver needed hospital treatment after he suffered a head injury in the shocking attack in Hove.
Emergency services were called to New Church Road, near the junction with Sackville Road, to reports of the driver being set upon by a cyclist after an altercation.
Brighton and Hove Buses managing director Martin Harris said: “We’re very unhappy about it.
“It’s a great concern to us and suffice to say we’ll be doing absolutely everything we can to assist police and make sure that action is taken against somebody who attacked a member of our staff.”
Mr Harris called the attack “shocking” and said he had not experienced anything this sinister since he joined as chief in April last year.
He said: “It’s very rare to have an incident of this seriousness but one is too many.
“We have and will continue to give police our full commitment so that we can bring the perpetrator to justice.”
The driver is not back on the road after his ordeal and his colleagues rallied around him during his recovery.
Mr Harris added: “There is a strong camaraderie within the business and they were very concerned about the driver, as were we as his employers.
“He’s doing much better.
“We supported him when he was taken to hospital and he will continue to get our full support as police continue their investigations.”
The attacker, who is described as a white man aged in his late 20s or early 30s, rode off in the direction of Portslade on his racing style road bike.
He was wearing a dark blue suit and carrying a leather shoulder bag when the attack happened at 1.10pm last Wednesday.
Police have released an image of a man they wish to speak to. A spokesman said the bus involved was a number 1A.
Anyone with any information is asked to contact police on 101 or email firstname.lastname@example.org. police.uk quoting serial 716 of 25/6