An officer at the front of the communal block of flats.
At this stage, the man has not been charged, police said.
A spokesman for Tayside division said: “A 31-year-old man has been arrested following a serious sexual assault on a 28-year-old woman at Colinton Place on Thursday February 28.
“The woman has been taken to Ninewells Hospital for treatment.
“Police inquires are ongoing, and at this time the man has not been charged.”
The police cordon at the back door of the close.
One woman said CID had asked her if she was aware of an incident on the ground floor.
Another man, who declined to be named, said there were around 10 police officers at the scene.
He added: “I saw the vehicles stationed on Saggar Street just after 1am.
“The officers were in the area that was cordoned off.”
