Keane scored three goals during his stay last season and Lambert may be tempted to repeat the deal.
Lambert said: "Robbie Keane is a brilliant player and has been over the years.
"When January gets closer I'll start to think about things. Is it something I would go for? I'm not sure because the team is the most important thing for me.
"If someone fits in with the group and has the desire to do it, and wants to do it, then I'll take a look at it."