The 49-year-old man was cycling along the cinder track, a path that connects Baylis School with Northern Road, in the vicinity of Villiers Road when he cycled past a group of six teenagers.
One of them hit him in the face and knocked him off his bike and the assault continued with at least two members of the group punching him in the head and face before he managed to escape.
Det Con Joshua Pitts, investigating the assault, said: "This appears to be a completely unprovoked attack, leaving a man with serious injuries. I therefore urge anyone with information to get in touch as soon as possible so that we can find those responsible and bring them to justice."
After the incident on Wednesday last week, the man was treated at Wexham Park Hospital and has since been released.
The teenager who initially attacked the man is white, in his late teens and about 6ft 2ins. He was wearing a light-coloured hooded top.
Detectives are particularly keen to speak to a woman who assisted the man after the assault.
Anyone with information can call DC Pitts on 08458 505505 or the Crimestoppers charity on 0800 555 111.