England's Geoff Parling is also in the running for a spot at the Suncorp Stadium on June 22 but 116-Test veteran Sharpe expects to see a Scottish and Irish combination in The Lions' boilerhouse in Brisbane.
"That surprised me a little bit," said Sharpe in relation to Warren Gatland's second row selection for the game against the Waratahs.
"I feel they'll go with Gray (for the first Test). He's played a couple of games in a row so they might be giving him his bit of rest.
"I think O'Connell will definitely be one. Alun Wyn Jones has been there and done it before and he's also a good lineout operator.
"(But) Richie Gray presents a different threat. He's taller, he's bigger and he runs a little bit more. He's a little bit more involved in the loose, which is something they may want if they are going to try and spread the game.
"That selection for the other lock will come down to how they want to play. Parling had a good game against the Reds. He did well against a Reds setpiece that was struggling, so I think he's put his best foot forward as well."
As for selection for the Qantas Wallabies second row, Sharpe is tipping Rob Simmons to wear his old shirt alongside recently re-appointed skipper James Horwill.
Simmons only started twice for his country last season despite the absence of the injured Horwill but he now appears likely to add to his tally of 23 Test caps.
Sharpe's much-heralded retirement in December initially saw Sitaleki Timani installed as favourite to fill his hugely-experienced shoes but the Waratahs' enforcer was last week ruled out of contention with a broken thumb.
Fellow Tah Kane Douglas remains in the mix, as does late call up Peter Kimlin, but it is 24-year-old Simmons who seems the front runner, even though he isn't best known for the physical approach favoured by Timani.
"Rob is one of the most athletic guys I've played with in terms of second rows," added Sharpe, who believes Simmons possesses the aerial abilities needed by the hosts if they pick a back row based on out and out scavengers and big, powerful ball carriers.
"He's a very skilful guy. He's very good technically as well around the paddock.
"He's been running the lineout for the Reds and he's done a good job of that. Out of all the second rowers currently in Australia, he's probably the one that, if he gets in the team, would organise the lineout. He's got one of those typical calling lock's analytical brains - that's probably the best way to describe it.
"He's a young guy coming through who has the capacity to really improve, and improve quickly. He's definitely going to be involved in this series one way or another.
"That's one of the things that the selectors have to way up, what they're looking for in that particular position - that balance as a back five is critical, both for Australia and The Lions.
"You've got to get that aerial ability balancing nicely. You can't pick three scavengers in the back row and then a big, abrasive lock like Sita (Timani) may have been. That comes down to the selection, which the coaches are going to sit down and talk about, probably today I'd say."
One man certain to start for the Qantas Wallabies is Horwill, a player who hasn't featured for Australia since the back end of 2011 but whose understanding of what it means to represent his country and his impact on his team-mates continues to impress Sharpe.
"James is a guy who works incredibly hard. He's very passionate and there's absolutely no way that he'd give up or let the team down.
"He plays with his heart on his sleeve, he plays hard and he's a guy who's always looking to go on the front foot. He's a great guy to be leading the team."
Nathan Sharpe was speaking to this website at an event organised by The British & Irish Lions' Principal Partner, HSBC.