"You would be mad to write off Wales in Cardiff, especially with the type of rugby they are playing at the moment. Look at Llanelli, they are the form team in the Heineken Cup," admitted O'Callaghan, who is set to win his 31st Test cap at the Millennium Stadium.
"Look at the Ospreys too, Welsh rugby is on a high. We will definitely have our work cut out for us in Cardiff."
Growing into his role in Ireland's second row, having played in all 11 Test matches in 2006, O'Callaghan recognises that Ireland will get nothing handed to them on a plate in this tournament, adding: "It's time for us to put our heads down, and get the get the work done, the hard work."
Losing a player of the calibre of Shane Horgan for the beginning of the Six Nations has dented Ireland's hopes, but with injury part and parcel of the professional game, O'Callaghan stressed the point that squad depth will be vital in the coming weeks.
"Shane is one of those fellas, as a forward, you love to have on your team," admitted the Corkman. "Because you look out and he's not going to take a backward step.
"In attack and defence, he goes after teams. If the ball isn't coming to him, he goes looking for it.
"Guys like that are priceless really, and he is a massive loss to the Irish team. But we've a strong squad and just have to deal with injuries like that. We've got some top quality backs and there are guys itching to get into the side."
Disappointing as last week's trio of Heineken Cup losses for the provinces were, the quick turnaround into a full-bloodied Six Nations campaign has meant little time for reflection for O'Callaghan on Munster's reversal against Leicester. However the players have seemingly refocused with ease.
With plenty of twists and turns ahead in a World Cup-dominated year, he added: "We've come into camp and parked our Munster, Ulster and Leinster caps and tuned into Irish mode. Everyone is tuned in for Wales. I think fellas are professional enough not to be looking back over things. We'll analyse that when we get back to our provinces."