The initial press release from Alpine, however, did not feature quotes from the driver himself, something that raised questions on the validity of the move.
It is understood that Alpine had an option on the Australian's future during the early part of the season but this elapsed at the end of July.
Piastri is believed to have signed a pre-contract deal with McLaren and the Contract Recognition Board is reported to have ruled that the arrangements with both teams are valid.
"The FIA's Driver Contract Recognition Board [CRB] was set up to deal with contract priority issues between drivers and F1 teams," said Ben Sulayem on social media.
"That's why we rely on their decision to resolve any conflict."
The @FiA's Driver Contract Recognition Board (CRB) was set up to deal with contract priority issues between drivers and @F1 teams. That's why we rely on their decision to resolve any conflict.