O'Neill and chief executive Peter Lawwell have been in talks with Barca president Joan Laporta and are reportedly set for discussions with several of the club's stars.
Barca boss Frank Rijkaard has been allowed to loosen the purse strings this summer - leaving a number of players sweating over their futures.
O'Neill's main target is thought to be Argentinian playmaker Juan Riquelme, who spent last season on loan at Celtic's Uefa Cup victors Villarreal.
The diminutive playmaker is wanted by Mexican outfit FC America but the move looks to be dead, as the player has indicated little interest in a move back to South America.
Midfielder Pablo Sanz Iniesta faces competition from recent arrivals Ludovic Giuly and Deco and is another likely to be deemed surplus to requirements.
Former Arsenal favourite Marc Overmars is a name in the frame and Spanish international Gabri also looks to be on his way out of Camp Nou.
Even the precociously gifted Xavi could face a Catalan exit and O'Neill is a known admirer of the Spanish international.
The final name to be linked to the Scottish giants is Mexican central defender Rafael Marquez - who is a near certainty to leave the club.
After a quiet summer in terms of arrivals at Celtic Park, midfielder Stephen Pearson has spoken of his delight at his manager's ambitious moves in the transfer market.
''It's good to know the manager has been looking at players of the quality of Xavi and Riquelme, who could easily be termed world class performers,'' he told the Daily Record.
''These are the big names we need. It seems strange there have been no signings but the manager obviously knows what he's doing.
''He's been through it all before but I think the fans are getting excited because they want to see new faces.
''We've lost major players like Henrik Larsson, Liam Miller and Johan Mjallby and the need is to strengthen the squad as a whole.''
