Thames Valley Police is appealing for witnesses following a robbery in Campbell Park.
The incident took place on Monday at about 1.30pm. It was the second robbery in the park in four days.
The victim, a 32-year-old man, was sitting drawing a picture by the statue in the park when he was approached by a man who asked the victim for money and to look at his phone.
When the victim refused, he was assaulted by the offender.
An altercation then took place and the offender called for help. Two other men arrived from nearby and also began to assault the victim before stealing his mobile phone and blue fabric wallet which contained a bank card, an ID card and cash.
The victim sustained bruising and cuts to the face, head and body.
The first offender is a black man, aged about 25, with a skinny build. He was wearing a dark blue hooded top and trousers, and wore a white dust mask around his mouth. He had a local accent and was about 6ft tall.
The other two offenders were also black men, and were wearing dark clothing.
Investigating officer detective constable Susan Russell said: “This incident happened in a park in daylight, so I am hoping that people saw it happen and can help by coming forward with information for our investigation.
Anyone with any information is asked to call Police on 101.