A Boeing 737 Max due to be delivered to Ryanair has had the model's name changed on the nose of the aircraft, it has emerged.
Photos shared on Twitter show a plane in Ryanair colours outside Boeing's manufacturing base, with the name 737 Max replaced by 737-8200.
It has fuelled speculation that the troubled Max will be rebranded after two fatal accidents led to a worldwide grounding.
Boeing and Ryanair have yet to comment.
No Max planes have flown since March after issues with its software were linked to crashes in Indonesia and Ethiopia, which killed 346 people.
Ryanair has 135 of the controversial Boeing models on order, the first five of which are due for delivery this autumn.
Before-and-after images of one of the Ryanair planes have been posted on Twitter account Woodys Aeroimages, which tracks Boeing production. The images show the Ryanair plane, a larger version of the Max 8, at Boeing's Renton plant in Washington state.
The tweets claimed the pictures showed the original model name had been dropped.
Boeing itself has not ruled out rebranding the 737 Max in future, while others have already taken to referring to it by another name.
At the Paris airshow last month, International Airlines Group, which owns British Airways, announced plans to buy 200 Max planes at a discount, referring to them as "B737 aircraft".
Boeing has yet to convince regulators that updates to its software are enough to ensure the Max's safety.
And last month the US Federal Aviation Administration, which must reapprove the jets for flight, uncovered a new flaw that Boeing estimates will take until at least September to fix.
On Sunday, American Airlines said it was extending for a fourth time cancellations of about 115 daily flights. The cancellations will now continue into early November due to the ongoing grounding of the 737 Max.
However, the firm added: "American Airlines remains confident that impending software updates to the Boeing 737 MAX, along with the new training elements Boeing is developing in coordination with our union partners, will lead to recertification of the aircraft this year."