Payne retired injured at half time in the Celtic League game v Cardiff Blues last Saturday, having been felled by a heavy high tackle. It has been reported that Payne is not suffering from concussion, however.
O'Callaghan injured his calf in training prior to the Llanelli game at the start of this month. The tear is taking longer than anticipated to heal as it is close to the achilles tendon. The player hasn't played a match since a Celtic League encounter with Connacht last April.
Coach Alan Gaffney expects to finalise his starting line-up on Thursday.
Munster:P Burke, C Cullen, P Devlin, J Kelly, R Henderson, A Horgan, J Holland, M Lawlor, R O'Gara, M Prendergast, P Stringer, J Storey. T Bowman, A Foley, J Flannery, M Horan, T Hogan, J Hayes, S Keogh, D Leamy, G McIlwham, P O'Connell, A Quinlan, F Sheahan, J Williams, D Wallace.