Busquets, 34, announced in May that he will be leaving the La Liga champions after 18 years at the club.
The midfielder will link up with Argentina forward Messi, 35, who confirmed this month he was moving to Inter Miami from Paris St-Germain.
Busquets and Messi spent 13 seasons together at Barca from 2008 to 2021.
They were part of a successful team which won three Champions Leagues, eight La Liga titles and six Copas del Rey.
Meanwhile, Kalidou Koulibaly has become the latest Chelsea player to move to Saudi Arabia after the defender completed a transfer to Al-Hilal for an undisclosed fee.
The centre-back, 32, joins Ruben Neves at the Saudi Pro League side following the Wolves midfielder’s £47m switch.
Chelsea midfielder N’Golo Kante has also agreed to sign for Saudi champions Al-Ittihad, while team-mate Edouard Mendy is close to joining Al-Ahli.
Koulibaly signed for Chelsea from Napoli last July on a four-year deal.
Though according to BBC Sports, Chelsea did not disclose how much Al-Hilal have paid for Koulibaly – but reports suggest it could be as much as £20m.
In another development, Sunderland have completed the signing of PSV Eindhoven defender Jenson Seelt for an undisclosed fee.
The 20-year-old, who has signed a five-year contract, has made one Eredivisie appearance, against PEC Zwolle in May 2022, and featured in matchday squads last season.
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Seelt has played for reserve side Jong PSV in the second tier on 63 occasions, 33 of which came last term.
He came through the Eindhoven club’s academy, which he joined in 2017.
Written by: Debby Eselebor
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