Ryanair's Michael O'Leary says IAG can "still come and talk to us" about its near 30pc Aer Lingus stake if the Government fails to make a decision on a sale.
The airline boss has claimed that the Government is the "only obstacle" to Aer Lingus being acquired by another operator such as IAG.
But Mr O'Leary added that Ryanair would be concerned about more than just the price IAG is willing to pay for Aer Lingus. IAG has indicated it is willing to pay €1.36bn for the Irish airline.
He said the Ryanair board would base its considerations on selling its Aer Lingus stake "not just in terms of price", but also on the plans IAG would have for Aer Lingus in the future.
"One of the big areas of discussion between ourselves and IAG will be what kind of competition remedies will IAG have to offer up to the European Commission in order to allow a takeover to take place," said Mr O'Leary. "That will also clearly be relevant."
The Government controls 25.1pc of Aer Lingus and is considering whether or not it should agree to sell it to IAG.
Mr O'Leary was speaking as he unveiled the latest planned changes that consumers will see at Ryanair, including new aircraft interiors, insurance products, uniforms and menus.
Ryanair has also made an application to the UK's Competition and Markets Authority (CMA) in an effort to reverse a previous decision by the watchdog to force Ryanair to reduce its stake in Aer Lingus to 5pc at most.
In 2013, the CMA's predecessor, the Competition Commission, ordered Ryanair to cut its Aer Lingus stake because it had concerns regarding competition in the UK, and because it believed Ryanair's position as a substantial Aer Lingus shareholder deterred other airlines from making a bid for the smaller rival.
But Ryanair's lawyers have told the CMA that its original decision is now flawed because IAG has tabled an offer to buy Aer Lingus.
"Ryanair's shareholding in Aer Lingus does not prevent Aer Lingus from merging with, being acquired by, or otherwise entering into combinations with other airlines, and which fatally undermine the lawfulness of the proposed divestment remedy," according to Ryanair's lawyers.
They added: "The reaction of the Irish Government to these (IAG) announcements has confirmed what Ryanair always said (and the Competition Commission dismissed), namely that the Irish Government, and not Ryanair, represented the only obstacle to Aer Lingus's combination with any other airline.
"Put bluntly, Ryanair's position has been entirely irrelevant to the events currently unfolding".
IAG chief executive Willie Walsh is due to meet Aer Lingus union representatives on Friday to thrash out more details about his plans for buying the airline. New Aer Lingus boss Stephen Kavanagh will also be at the meeting.