Barcelona have confirmed their Twitter account was hacked after a message appeared to announce the signing of Angel Di Maria from Paris Saint-Germain.
The Catalans have featured heavily in this summer's transfer window, notably receiving a world-record fee from PSG for Neymar.
And tweets sent from the club's social media account overnight suggested they had been involved in another huge deal.
At 3.07am, the message "Welcome Angel Di Maria to FC Barcelona! #DiMariaFCB" appeared on the club's Twitter feed.
Before a frenzy was allowed to develop, that was swiftly followed by "Hi FC Barcelona, it's OurMine security group, please contact us and sorry for the hoax!"
OurMine security group are a security hacker group who have accessed celebrity internet accounts in the past.
And, just after 5am, Barcelona responded to the alleged hoax. "Our accounts have been hacked tonight," a tweet read.
"We're working to solve the problem as soon as possible. Thanks for your patience."
The hacking episode comes days after Sky Sports Spanish football expert Guillem Balague revealed Barca had turned their attention to Di Maria after Liverpool's reluctance to sell Philippe Coutinho.