Officers were called to Zinzan Street close to the Oxford Road junction shortly after 7.30pm last night when a fight broke out among a group of up to 12 men.
The 32-year-old victim was taken to the Royal Berkshire Hospital and will be transferred to the John Radcliffe Hospital in Oxford later today to treat his injuries.
Police believe his attackers may have been carrying weapons and they are studying a pile of broken bricks found at the scene which could have been used during the fight.
A 28-year-old man from Zinzan Street who awoke to find police had sealed off a section of the road outside his house said: "I can't believe, it especially as lots of people would be coming home from work at that time. I'm worried for our safety."
Detective Sergeant Ashley Hannibal said: "Officers and PCSOs will be carrying out reassurance patrols and enquiries in the area and we would like to speak to anyone who may have witnessed what happened."
Witnesses should contact police on 101 or Crimestoppers anonymously on 0800 555 111.