The incident happened at around 7.15am when the man was hit on the head with a metal bar by two men in Tubb Close.
The offenders left the area in the direction of Ruckeene Way.
The victim, was taken to hospital with a head injury and has since been discharged. The offenders are described as two white men, aged in their twenties. They were wearing dark hooded tops and dark trousers.
One offender was around 5ft 4ins tall of stocky build with a beard. The other was around 6ft tall and of slim build.
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Investigating officer PC Abigail Sharman based at Bicester police station, said: "This was an unprovoked assault on a man who had to be taken to hospital with a serious laceration to his head.
"Thankfully, it is thought the victim will make a full recovery but this so easily could have been much worse. I would like anyone with information about this incident to get in touch.
"I would ask anyone with dash-cam or CCTV in the area to check this for anything unusual around this time and pass it to police.
"If you saw anything with regards to this incident or know anything about it, please contact the non-emergency number 101 or make a report online quoting the reference 43200017061.
"If you would prefer to remain 100 per cent anonymous, please call the independent charity Crimestoppers on 0800 555 1."