An incident on a Ryanair flight which saw a passenger partially sucked out of a plane window may have been caused by "foreign object damage" to an engine, said the airline's boss.

Michael O'Leary said an initial investigation into the incident on 10 July between Greece and Germany suggests "it looks like a foreign object damage to the engine on takeoff at Thessaloniki but ... we can't say that definitively".

He insisted that the engine on the 18-year-old Boeing 737 plane had been fully serviced and overhauled in the past two years.

Serbian national Ljubisa Karović's head and right shoulder were sucked out of the plane's window, leaving him "seriously injured and in shock".

His wife Svetlana Grković Maksimović told BBC Serbia that she and two other passengers held on to his legs for several minutes.

She said: "We pulled him back together. His entire face was deformed and blood was pouring from his nose and mouth."

He was taken to hospital after the plane made an emergency landing.

Passengers told local media they heard "some kind of explosion" on board.

The aircraft was operated by Ryanair's subsidiary Malta Air.

Confirmation that the damage was caused by an external object could affect Ryanair or Boeing's liabilities over the incident.

The US National Transportation Safety Board (NTSB) is investigating. O'Leary said that a draft report would be issued in about 28 days.