The 31-year-old former Rangers star is expected to put pen to paper on Monday after the clubs agreed a fee, believed to be up to £1million.
"We are just waiting on a bit international documentation," manager Malky Mackay told the club's official website.
"We've agreed the fee, we've agreed his terms and the medical has been passed. He's been training with us and he has gone up this weekend to collect some stuff and bring his family down."
"We are doing the medical with him at the moment and he should sign on Monday," added Mackay.