The 37-year-old wheelchair racer, who won four gold medals at the London Paralympics, announced his retirement from track racing after an unsuccessful Paralympic Games in Rio last year.
He said April's London Marathon would be his final road race.
British Athletics says it is puzzled by Weir's comments, which came in a series of tweets on Tuesday.
"I have just retired from GB. I will still be at the London Marathon this year," wrote Weir.
A six-time world champion, he said he felt like he had been "stabbed in the back" after he crashed out of the marathon in Rio, his last ever Paralympic event.
The BBC has attempted to contact him for comment.
Six-time Paralympic champion David Weir says he will never wear a Great Britain vest again, adding he feels "let down".