The Ireland international sat pitchside in Brisbane on Saturday and joined in all the pre-match rituals before failing to appear during the tourists' 23-21 win over the Wallabies.
However, O'Brien is targeting a positive result as well as a strong individual display that would help mount his claim for a spot in the Test outfit.
"Yeah, it was difficult enough. I had to prepare like I was going to play just in case anything did happen. Doing the warm-up and feeling that buzz and then sitting on your chair for the rest of the match is disappointing, obviously," O'Brien told the official Lions website.
"As Lyds (Dan Lydiate) has said, we all have a chance to stake a claim again and go out and show what we can do. The coaches are telling us this and we have to put our trust in them as well.
"We can only look after ourselves. We have another match to play and there is no point going out thinking we haven't got a chance. That will only affect your performance so you have to do what you can do and do the best you can do in every opportunity you get in a Lions jersey."
The Lions get underway against the Melbourne Rebels at 10.40am on Tuesday.