O'Callaghan will overtake Ronan O'Gara with the most appearances after a stellar career with the province that is set to continue until 2016 after the lock forward recently signed a two-year contract extension.
With the Ireland team not playing this weekend, Tommy O'Donnell and Felix Jones returned to train with the squad.
Donnacha Ryan made the step up to full training as he continues to regain full fitness following a knee injury with Ivan Dineen also back in full training after injuring his ankle playing for Munster A against Nottingham.
Paddy Butler will return to training later in the week after injuring his neck while playing for Shannon in January.
It's good news for Keith Earls as the Limerick man is on target with his rehab and will be looking to return in the next 4-6 weeks.
Damien Varley(delayed concussion) is following the IRB return to play protocols and is set to return to training next week.
Niall Scannell suffered a hyper-extension of his right elbow in training last week and will be out for up to eight weeks.
Luke O'Dea sustained a grade one lateral ligament sprain during Munster A's win against Connacht Eagles on Friday and is rehabbing.
Longer-term absentees Niall Ronan and Mike Sherry are continuing with their rehabilitation programmes
There's good news off the playing field as it has been confirmed that Team Manager Niall O'Donovan will stay on in his role into next season.
O'Donovan has been Team Manager since 2012 when he took over from Shaun Payne to resume an association with the province that began in 1997.
Tickets are available here for Saturday's RaboDirect PRO12 clash between Munster and Zebre at Musgrave Park (ko 6:45pm).