"We are very optimistic about the possibility of closing a goalkeeper deal between today and tomorrow," Garces told MARCA, confirming the Turkey international is set to become Celta's fifth summer signing on what is expected to be a season-long loan.
The 28-year-old has fallen behind Senne Lammens in United's pecking order after a difficult run as first-choice goalkeeper last season, in which he failed to keep a clean sheet in six Premier League appearances, and has been further squeezed by Karl Darlow's arrival as back-up.
Celta Vigo manager Claudio Giraldez has been pushing for additional competition for Ionut Radu between the posts, with the Romanian dealing with a muscular injury heading into the new campaign.
Manchester United are believed to prefer a permanent sale but have so far been unable to secure one given Bayindir's wages, with the loan structure reportedly unlikely to generate an immediate fee for United, who retain the option to extend his contract, currently set to expire in 2027, by a further year.
A forward is expected to follow as Celta's sixth and final arrival of the window, though Garces cautioned that deal remains further away.
"The one for the forward is a bit greener, although I also hope to have news soon," he said. Celta are also working to move on several fringe players, including Carles Perez, Unai Nunez, Carlos Dominguez and Manu Fernandez.
"As Claudio has mentioned, the players have known since May what their status is within the squad. I know they are receiving calls and offers and they are assessing them to see when a satisfactory one arrives, and then it can move," Garces explained, adding that the timing of any exits "rests more in their court than in ours."
Bayindir joined United from Fenerbahce for an initial €5m in September 2023 and made 166 appearances during a five-year spell in Turkey before that move, keeping 53 clean sheets. Celta finished sixth in LaLiga last season and are targeting a further push up the table, with reinforcing the goalkeeping department seen as a priority before the position is tested by the demands of a longer campaign.
The move would represent a fresh start for Bayindir, who began last season as United's first-choice goalkeeper but was gradually usurped by Senne Lammens after conceding 11 goals without a clean sheet in six Premier League outings.
He returned to the matchday squad for United's friendly against Atletico Madrid over the weekend but was overlooked in favour of third-choice Tom Heaton, read as further confirmation his future lies away from Old Trafford.