The 36-year-old defender has been without a club since leaving Tottenham Hotspur at the end of last season.
Holloway has admitted that there have only been initial talks made with the former France international.
"We are a long way off a deal with him, but I met him. Whether we can ever come to a deal I do not know," Holloway told Sky Sports News.
"He was a very nice man and he admitted he is only 50 per cent fit, which might be a problem."
Queens Park Rangers and Australian side Melbourne Victory are also reportedly interested in signing Gallas.