The 32-year-old tweeted that his flight - booked by the Ryder Cup team - was altered due to a lack of staff on board.
The Spaniard wrote: "I hardly ever criticize, but been downgraded on my flight because @ British_Airways screwed up with their number of crew members."
The airline messaged an apology to the golfer and offered a partial refund, to which he replied: "I didn't pay for my ticket, @ RyderCupEurope did. I hope you guys get the full refund. Pitiful service by @ British_Airways.
"And I'm totally ok with flying economy, I always do when in Europe. Just pissed off at the little answers I get from @ British_Airways.
"'Not enough crew to assist in case of emergency', that's why I was downgraded? Really? #stupidexcuse @British_Airways. One crew not enough for aprox 15 passengers in business?But 2 enough for more than 50 in economy? @British_Airways Who taught you math?"
The Ryder Cup between Europe and the USA will get underway on September 30.