The former Newcastle United striker hasn't played since November.
But Ranger, a free agent after the Football League intervened and terminated his Blackpool contract, is training with the Championship club, according to the Sheffield Star.
Ranger spent more than five years at Newcastle.
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The 24-year-old left St James's Park by "mutual consent" in 2013 after the club lost patience with him following a number of off-the-field incidents.
Ranger recently issued a statement on Twitter admitting he "should have been a better role model".
"I just want to take the time out to write this post as I feel like I need to get this off my chest," he wrote. "I have seen 2 of my good friends pass away in a short space of time.
"Whilst over coming this it has made me realise life really is too short and have really been taking things for granted.
"I would like to use this opportunity to thank, Southampton, Newcastle, Swindon and Blackpool for giving me the chance to experience the dream of being a professional footballer.
"To add to this I would like to apologise to every one at these clubs, including management, players, staff and fans. I should have given more and been a better role model."