Ryanair is likely to feed passengers to the Aer Lingus long-haul network as part of what would be an unprecedented formal agreement between the two former arch rivals, according to IAG chief executive Willie Walsh.
The two airlines have held high-level talks at various stages over the past year or more on a so-called interlining model.
It could see Ryanair feeding passengers from its extensive network at Dublin to Aer Lingus routes serving North America.
Speaking yesterday en route to San Jose in California, as British Airways launched an inaugural flight to the city from Heathrow, Mr Walsh said that while nothing concrete has been agreed between Aer Lingus and Ryanair, a feeder agreement is almost certain to be inked at some stage.
"I'd be surprised if we don't reach agreement with them at some point," said Mr Walsh.
"There were very advanced talks with Aer Lingus at a high level. I briefly discussed it with Michael (O'Leary), but we had senior people in Aer Lingus discuss it with senior people in Ryanair. We've no objection to working with them. If customers want to connect from a Ryanair flight, we're very happy to do that. There were some commercial issues, but I think it's workable."
IAG, which also owns British Airways, Iberia and Vueling, acquired Aer Lingus last year for €1.36bn. Ryanair had tried three times to buy the rival airline but was blocked by Brussels.
Mr Walsh said IAG remains open to the feeder idea and that there's "no objection to it".
"It would be more of an option for Aer Lingus (than BA or Iberia) because of the Ryanair network at Dublin Airport," he said. "If we can reach a commercial agreement with Ryanair, and if customers want to do it: absolutely, no problem.
"Ryanair has an interesting network into Dublin from cities not served by Aer Lingus, and unlikely to be served by Aer Lingus. So, anything that improves the connectivity onto our transatlantic (network) is something that would be attractive for us."
Mr Walsh said Ryanair is likely to only provide feeder passengers to other airlines "where it's convenient for Ryanair".
"They're not going to change their schedule or their modus operandi to facilitate someone else," he said.
Mr Walsh added that Ryanair's change to its customer service model has been "stunning".
The IAG chief executive said he doesn't agree with Mr O'Leary's prediction that legacy carriers such as British Airways or Lufthansa will eventually cull their short-haul networks.
Last month, Mr O'Leary said Ryanair will trial interlining at London Stansted and Barcelona later this summer.
He said that would allow passengers travelling from cities that may not have a major Ryanair route network, such as Belfast, to connect to other Ryanair services at Stansted to onwards destinations.