O'Neill is yet to speak to the Aston Villa keeper, currently on loan at Middlesbrough, following his decision to retire from international football last summer after 125 caps.
Ireland's next game is not until 5 March, when they take on Serbia in a friendly at the Aviva Stadium, and O'Neill is keen to have as many players as possible at his disposal.
"I haven't spoken to Shay but I would like to at some stage, if he says 'I'm back'," said O'Neill.
"But I am having a conversation here about somebody I haven't actually spoken to.
"I know Shay and I've spoken to him a number of times but that was before I took the job on.
"I may be a million miles out of my ground because he may have no intention of coming back, but I certainly wouldn't discount it if I'd had that conversation and he was thinking about coming back."
Former Villa and Sunderland boss O'Neill has promised to keep an open mind on players, including those discarded by former national boss Giovanni Trapattoni.
He is also keen to introduce new talent to the squad, including those who may have represented other countries below senior level.
"Some players the previous manager maybe felt weren't his cup of tea, I might disagree on and vice versa, that's always the case as a manager," added O'Neill.
"One or two are doing well at the moment and I would like to bring them into the squad and there are other younger lads that I've been quietly impressed with.
"I don't want to individualise now but young Nathan Redmond (a current England U21) plays at Norwich and I'm aware there might be some kind of connection."