Unai Emery's official website appeared to confirm him as the new Arsenal manager on Tuesday.
The former Paris Saint-Germain coach's site showed a graphic with the Gunners' logo and the statement: "Proud to be part of the Arsenal family."
However, the page went down and displayed an error message soon after news of the upload spread. His verified Twitter account still listed him as the coach of PSG.
Emery emerged as the frontrunner to succeed Arsene Wenger, whose 22-year reign came to an end at the conclusion of the club's Premier League campaign on May 13, following links to Mikel Arteta.
The former Sevilla boss spent the last two seasons at PSG, winning five major trophies, but did not have his contract extended and was replaced by Thomas Tuchel.
Emery's time at the Parc des Princes will ultimately be remembered as somewhat unsatisfactory, PSG having been dethroned by Monaco in Ligue 1 in his first campaign and twice failing to get beyond the last 16 of the Champions League.
Arsenal will again not be in the Champions League in 2018-19, Wenger having been unable to secure qualification in his final two seasons at the helm.