The Ireland centre is firm favourite to take over from an injured Sam Warburton in Saturday's Sydney showdown against Australia.
Wales flanker Warburton suffered what the Lions described as a "significant" hamstring tear during the 16-15 second Test defeat in Melbourne three days ago.
Sean O'Brien is his likely back-row replacement, with 34-year-old O'Driscoll poised for leadership duties as the Lions chase a first Test series victory since 1997.
Lions head coach Warren Gatland is due to name the starting line-up in Noosa on Wednesday, with centre Jamie Roberts and prop Alex Corbisiero expected to be in contention for places after recovering from hamstring and calf muscle injuries, respectively.
O'Driscoll, meanwhile, will end a fourth Lions tour of duty stretching back to 2001 hoping he can fill one missing entry in a career portfolio packed with trophy successes.
It would be his ninth Lions Test match appearance, putting him level with current tour manager Andy Irvine and Syd Millar, and one ahead of players like Martin Johnson, Jim Telfer, JPR Williams and Jeremy Guscott.
"They have been two incredibly keenly-contested games. Both of them should probably have gone the other way than they did, and it now culminates with a winner-takes-all," O'Driscoll said.
"We knew we were never going to get it easy against Australia, and it has been proved.
"You kind of think how scenarios could be different - having a series in the bag, rather than one still to go and fight for.
"But then after a couple of days you just have to have the ability to shelve it and focus on the target. One more 80 minutes this season is all that is asked of everyone in the squad - the 80 minutes of their lives.
"People talk about the momentum going with the team that wins that second Test, and I would have agreed with it in 2001 because it was a comfortable victory they (Australia) had then.
"But just the way the two games have gone, with two points between us in the first one and one point in the second one, just shows how tight it is. I think the team that turns up on Saturday and gets some momentum from early in the game will get the upper hand.
"There is always a mental toll in games of this magnitude. Thankfully, you do get seven days to try to get over one game and have the building process for the next one.
"This game is very much mental as much as it is physical, and all the more so when you play opposition three weeks in a row."