Ryanair CEO Michael O'Leary is livid over Boeing's delays to bring its 737 Max plane back to service after Boeing halted deliveries of the plane earlier this year.

"I am concerned that the Max return to service is slipping," O'Leary said in a conference call Monday.

O’Leary said Ryanair may not have planes ready by next summer unless Boeing "gets its s--- together."

Boeing took 737 Max jets out of service in March after crashes in Indonesia and Ethiopia which happened within five months of each other and killed a total of 346 people. The crashes were possibly caused by a sensor issue in the plane.

The company has halted its deliveries of the plane, which has disrupted Ryanair's business plans. O'Leary hoped to have 58 Max 737 planes operating by next summer.

"It may well move to 20, it could move to 10, and it could move to zero if Boeing doesn't get it's sh--- together with the regulator," he said.

A delay could result in the growth rate to decrease to 5 million from 10 million passengers.

Boeing is still in negotiations with safety regulators on when to proceed with its deliveries of the 737 Max. It's still unclear when regulators will allow the planes to fly again.

The halt in deliveries has also affected other airlines, such as U.S.-based airline company American Airlines which said the grounding will cost the company $400 million in pretax earnings this year.

Southwest Airlines, a low-cost U.S. airline, has warned travelers that grounding of the 737 Max will result in travel disruptions during the holiday season this year.

Ryanair is a popular low-cost airline based in Ireland. Ryanair planes operate on a tight schedule and charge for amenities such as food in order to keep ticket prices down and remain profitable. The company also requires expensive fees for baggage.

O'Leary is one of Ireland's wealthiest businessmen and has frequently made controversial comments to the press.

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