A teenage boy was stabbed in the leg as he fought back against a man who tried to steal his mobile phone.
The 16-year-old was approached by a man on a patch of wasteland near Kassam Stadium.
The man threatened him with a knife then tried to steal his mobile phone.
He refused and in the struggle the teenager suffered a stab wound to his thigh which needed stitches.
Police are appealing for a dog walker who was in the area at the time and may have witnessed the attack to come forward.
Dc Simon Beaton, of Oxford Robbery Team, said: "Shortly before the incident a man walking what appears to be an English Sheep dog walked past the offender. I appeal to this man to get in contact with police as he may be able to assist our inquiries.
"I also appeal to two white women who were with the offender walking across the car park near to Ozone Health and Fitness and Gala Bingo to contact police."
The attack happened shortly before 4pm on Monday, April 14, but police have only just released details.
The attacker is described as black, aged between 17 and 18-years-old, and was wearing a red and black anorak.
Anyone with information should contact police on 08458 505505 or speak anonymously to Crimestoppers on 0800 555111.
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