After being outplayed by New Zealand in their 21-3 defeat in Christchurch on Saturday, as well as losing to the New Zealand Maori and producing some lacklustre showings against the provincial teams, the Lions desperately need to stamp their authority on a game against second division opponents, especially with the crucial second Test in Wellington just days away.
"I think the main thing from Saturday is that people feel they underperformed. You can come off the pitch after giving your all and losing and you won't feel as bad as going out and not performing," O'Callaghan explained.
"When you come off the pitch and you feel like you left things behind, you've regrets, I think that is the big disappointment for those lads [that played on Saturday]. That's why it is so important on Tuesday.
"It was very disappointing last Saturday and the guys that are lucky enough to pull on the shirts on Tuesday will have the wishes of the whole squad to get this team back winning."
The Lions have also had to deal with losing their captain Brian O'Driscoll.
The Leinster man was forced out of the tour with a dislocated shoulder in the opening moments of the Test after being up-ended by All Blacks captain Tana Umaga and Keven Mealamu.
O'Callaghan admitted O'Driscoll's absence would be keenly felt - and not just on the pitch.
"Brian is a friend of everyone in the squad as well. You hurt for him as a friend as well as a captain and player. It was disappointing to lose such an important fella.
"He's a great rugby captain and also a great leader and to lose a fella like that is gutting."
O'Driscoll's departure and that of loose forward Richard Hill with a knee injury were not the only disappointments on a bitterly cold night in Christchurch.
The line-outs were poor for the Lions in the Test match with All Blacks duo Chris Jack and Ali Williams in command, stealing 10 Lions throws as Shane Byrne failed to find his target.
But O'Callaghan stressed that it was not just down to the hooker to ensure the line-outs functioned well and that the forwards as a unit had collectively taken responsibility and had been working hard to eradicate the problems.
"Line-outs are a team thing. An awful lot of pressure can come on hookers if things aren't going right. A good team takes it that we are all there to take it on the chin.
"They are working hard at the videos they are looking at calls and working hard to get it right. You'd expect no less from the type of player we have in this squad."