The former Newcastle forward has been in fine form since joining the Robins in the summer but, after being given leave by the club to deal with personal issues, Ranger has not turned up to training.
When asked about the 22-year-old's whereabouts, Cooper told BBC Wiltshire: "I don't know. That's all I'm prepared to say.
"He was never going to play on Tuesday (in their 2-1 win over Wycombe) but he was supposed to be in for training today (Thursday).
"But people should be concentrating on the players who played on Tuesday and that will play on Saturday."