Holloway has held talks with the Frenchman, who is available as a free agent after he was released by Tottenham.
The 36-year-old admitted to Holloway that he was only "50% fit", but the Eagles boss has not ruled out a move for the centre-half if terms can be agreed.
"We met him on Wednesday. I don't know yet if we can do a deal," Holloway said of Gallas, who has also attracted interest from Melbourne Victory.
"He was a very nice man and he admitted he's only 50 per cent fit which might be a problem. We're 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 also confirmed that he was lining up a bid for Reading winger Jimmy Kebe after he was given permission to talk to Palace by boss Nigel Adkins.
"He's one of the ones we're trying to pursue," Holloway added. "I was allowed to speak to Jimmy at about half 11 on Wednesday night. I don't know where we are with that."