The Scotland international arrived at Ashton Gate two weeks ago in order to regain full match fitness after almost a year out with a broken metatarsal.
The 31-year-old told the Bristol Evening Post: "I am here just for a month. The aim is to play some games. As for the future, I couldn't tell you. We will address it later in the month.
"I am keeping my head down and getting match fitness and, hopefully, I will score a few goals along the way.
"This has been the most frustrating spell of my career. But that is football for you and you have to take it on the chin and put a positive spin on it."