Officers are appealing for witnesses following the assault around 9.30am this morning.
The woman, in her 30s, was walking through Great Copse Woods between High Lawn Way and Middle Park Way when she was grabbed and pulled to the floor by a man she did not know.
She did not suffer any injuries. The man then fled the scene on foot.
He is white, in his 30s, with short hair or balding and wearing a light blue hooded top, blue jeans and yellow Timberland shoes.
PC Judith Clacey said: ‘We are appealing for any witnesses to come forward who may have seen what happened this morning or saw a man matching this description in the area at this time.
‘The assault took place near to the Middle Park Way exit, but the man was seen at the entrance near High Lawn Way beforehand.
‘We are keen to trace a woman who was walking her dog and walked past the victim and the offender just before the assault took place.’
She added: ‘I would like to remind members of the public to remain vigilant when walking through this area of woodland and avoid using remote paths, particularly when walking alone.
‘Please report any suspicious incidents to the police.’
Anyone with information should call PC Clacey on 101, quoting 44170084115.