It promises to be tough challenge for Cheika, given that he is without 10 players currently in the Australia camp preparing for next week's first Test and a further six on the injured list.
But Lions flanker O'Brien said: ''I know 'Cheiks' very well with him being at Leinster. He is an animated character as well, so I am sure he will have them fired up and wanting to be really aggressive and come hard at us."
He added: ''We are getting closer and closer to the Test games, and teams are going to try and come at us a little bit harder. The Waratahs will be no different.
''It's going to be a very tough game, and whatever side is picked for the Lions we are going to have our hands full at the start of the game again. 'They are really going to come at us out of the blocks and try and hurt us a little bit, so it's going to be massively intense again.''
Head coach Warren Gatland will name his starting line-up for the Waratahs encounter on Thursday.
Some previous Lions coaches have used the final Saturday game before the first international to give the probable Test side a run-out, but it is not thought Gatland will go entirely down that route.
Asked if he expected the Test team to feature this weekend, O'Brien added:
''Your guess is as good as mine. I don't think so, but who knows?
''Every week you could say is this the Test team? But it is all up in the air in every position, and we are just trying to do our own jobs and keep the head down and the coaches will pick the Test side when it comes to it. 'It's getting towards the business end of it, and it is exciting.''