The 32-year-old scored three goals for the Villans during a temporary spell with the club a year ago.
"Robbie Keane is a brilliant player and has been over the years," Lambert told reporters.
"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."
Keane is currently featuring for the Galaxy in the MLS playoffs.