Stephen Prosser, 51, from Penygraig, South Wales, told Pontypridd County Court on Friday that British Airways cabin crew ignored his warnings he would be injured if he was forced to sit next to the man, the Press Association reported.
Prosser, a freelance civil engineer, described the individual as being “extremely large,” 6 feet 4 and more than 300 pounds.
“He was that large that he had to force his buttocks between the arm rests of the seats,” Prosser said.
The man sat “with his knees wedged against the seat in front and the rest of his body was over spilling into my seat by some inches” on the flight from Bangkok to London in January 2016, Prosser said.
“I was immediately aware that this was going to be problematic for me and I could feel the weight of his pure bulk putting lateral pressure on my upper body. This forced me into a position of unnatural posture,” PA reported him as saying.
Prosser, who is 5 foot 3, claims he suffered nerve damage and a pelvic injury, leaving him with a continual back spasm.
He added that he had to visit a chiropractor for two years and to limit his work for three months.
Prosser said he complained to the crew but was told there were no other seats on the Boeing 777.
Asked in court whether he complained directly to the passenger, Prosser said he “didn’t want to get into a confrontation with him,” and added that the passenger seemed “self-conscious.”
Prosser’s claims were questioned by Timothy Salisbury, representing British Airways, who said the claimant was “exaggerating” in comparing the passenger to late New Zealand rugby player Jonah Lomu.
Chris McLindon, the customer service manager on board the flight, said in a witness statement reported by the BBC that he had “very rarely, if ever” dealt with such a complaint.
He added that Prosser did not appear to be in discomfort and was at times asleep during the flight.
“I regularly walked down the aisle and Mr. Prosser was not sat in an unnatural position for an economy seat,” he said.
“When Mr. Prosser left the aircraft, I watched him walk down the jetty in a perfectly normal manner and showed no signs of injury.”
A spokeswoman for British Airways said the company is resisting the claims, but declined to comment further, the BBC said.