Arsenal defender Campbell impressed by Celtic tour
The veteran defender was at Celtic Park as Hoops boss Neil Lennon stepped up his efforts to recruit the 35-year-old.
Campbell spent five years at Arsenal and impressed during his second spell with the Gunners after returning on a short-term deal in January.
He is now a free agent and Celtic are reportedly set to offer him a two-year deal to make the switch to the Clydesdale Bank Premier League, a move he has so far refused to rule out.
Speaking earlier this month, Campbell said: "Football's very important to me and I would give Celtic everything if I sign."