With the 24-year-old playing backup to the likes of Martin Odegaard and Bukayo Saka in the Arsenal attack, his opportunities for starts have been limited in the past 12 months.
Even though Arsenal are lacking genuine cover and competition for Saka on the right, Vieira was given the green light to return to Porto, where he rose to prominence before joining the Gunners in 2022.
The Dragons confirmed the signing of the playmaker on Tuesday, but there was interestingly no announcement from Arsenal, who prioritised Mikel Merino content following the Spaniard's move from Real Sociedad.
However, the North London giants have now finally released their own statement, confirming that Vieira will spend the entirety of the season with Porto, who are not believed to have an option or obligation to make his return permanent.
Vieira takes number 10 shirt at Porto
"Fabio Vieira has joined Portuguese side FC Porto on loan for the 2024/25 season. We wish Fabio all the best on loan this season with Porto. The loan deal is subject to the completion of regulatory processes," Arsenal said.
During his first spell in the Porto senior team, Vieira inherited the number 50 shirt, but the 24-year-old will now don the iconic playmaker's 10 for the Portuguese titans, vacated by Francisco Conceicao's exit to Juventus.
Revered names such as James Rodriguez, Deco and Ricardo Quaresma have previously sported the number 10 for Porto, whom Vieira recorded 10 goals and 18 assists for in 76 matches during his first spell at the club.
No player registered more assists than Vieira's 14 in the 2021-22 Primeira Liga season, and the 24-year-old hit the ground running at Arsenal with a terrific long-range strike against Brentford at the Gtech Community Stadium.
Vieira has failed to kick on since, though, only recording three goals and nine assists in 49 Gunners appearances, but he still has three years left to run on his contract at the Emirates Stadium.
What other business could Arsenal do before transfer deadline?
With Merino, Riccardo Calafiori and David Raya joining on permanent deals this summer, the bulk of Arsenal's remaining business is likely to be focused on outgoings, although they are noticeably short out wide.
Rumours continue to swirl surrounding late swoops for Athletic Bilbao's Nico Williams and Bayern Munich's Kingsley Coman, and a space will open up for one of them if Reiss Nelson also departs in the coming days.
However, a big-money transfer for either is not expected to materialise within 48 hours, so Mikel Arteta may make a concerted effort to keep hold of Nelson lest he risk a few months with no backup to Saka.
Two other home-grown players are on the verge of departing, though, as Eddie Nketiah is finalising a move to Crystal Palace, while an £18m deal has apparently been agreed with Southampton for the transfer of Aaron Ramsdale.
Decisions regarding the futures of Kieran Tierney and Jakub Kiwior could go down to the wire as well, although the former's Euro 2024 injury could scupper his hopes of an exit.