Allardyce said: "Campo is flying in from Madrid and we are looking at a loan deal this season, rather than a two-year deal which we discussed before.
"It looks like he is going to accept that although we have not finished it off yet.
"He will have a quick medical and hopefully train with the boys tomorrow prior to Sunday's game."
If talks go well and a deal is finalised, Allardyce could include Campo in the squad for Boltons home game with Aston Villa on Sunday.
"I need to talk to him at great length first to find out how many competitive games he has played," said the Bolton boss.