DUBLIN (Reuters) - Ryanair (>> Ryanair Holdings plc) is unlikely to agree to sell its 30 percent stake in Irish airline Aer Lingus (>> Aer Lingus Group Plc) until after an European Union competition probe that could take months, Chief Executive Michael O'Leary told Reuters on Thursday.

British Airways owner International Airlines Group's (>> International Consolidated Airlns Grp SA) proposed 1.36 billion euro ($1.53 billion) offer for Aer Lingus was recommended by the Irish airline's board in January, but the deal is conditional upon winning support from Ryanair.

Ryanair had been expected to make a decision after it receives a formal offer from IAG later this month, but if it waits for the EU, the process could drag on until the end of the year.

"The EU approval I suspect would happen beforehand," O'Leary said, when asked if Ryanair would wait for the EU before making its decision.

"If an offer document is submitted by the end of June, on EU approval, you'd expect the process to be complete before the end of the year one way or the other," he added.

O'Leary said he did not expect Thursday's "final order" by Britain's competition and markets authority for Ryanair to sell most of its stake in Aer Lingus would impact on negotiations with IAG.

He said he thought legal action being planned by Ryanair "certainly rules out a forced divestment in the next 6-12 months."

He also refused to rule out a renegotiation of IAG's 2.55 euro per share offer price.

"There is always the potential that the price could change, but if the price changed it would change for all shareholders," he said.

IAG CEO Willie Walsh said in May that 2.55 euros was "the limit which we are prepared to offer."

(Reporting by Conor Humphries, Editing by William Hardy and Mark Potter)

By Conor Humphries