IAG's shares were advancing on Friday after the revelation that Qatar Airways had purchased a 9.99% stake in the airline, though broker Liberum reckons that a full takeover of the Anglo-Spanish group is "highly unlikely".Qatar Airways, which already has a relationship with IAG through the Oneworld alliance, said it wants to strengthen existing commercial ties with the company.The Doha-based group, which is now the largest shareholder in IAG, said it "may consider increasing its stake further over time"."However, Qatar has no current intention for its stake to exceed the current level. This stake appears to have been acquired in the market, and it is certainly not the result of new shares being issued," Liberum said,"With this recent buying pressure removed, the share price may weaken."While the broker acknowledged that the investment may prompt takeover speculation, it said this was not likely to happen "due to the ownership restrictions on non-EU shareholders which are required to ensure that IAG's airlines retain their traffic rights".Liberum kept a 'buy' rating on the stock, which had drop 1.3% to 556.5p by 10:00 following a positive start.