Nottingham Forest are discussing a fee reported at around £8m for the 25-year-old, though other reporting in Spain has put the figure closer to €15m (roughly £12.8m), split evenly between Celta Vigo and Real Madrid under a sell-on clause retained from Rueda's academy days at the Bernabéu.
The move has not been straightforward: Celta manager Claudio Giráldez had publicly insisted just days earlier that a departure "hasn't even crossed my mind," and reports in Spain suggested Celta briefly withdrew their approval for the sale before talks resumed.
Rueda made his breakthrough last season, playing 26 LaLiga matches and 11 in the Europa League as Celta reached the quarter-finals.
Elsewhere, Forest have been rebuffed in their pursuit of a different full-back. Tottenham enquired about Neco Williams, but the Wales international is expected to stay at the City Ground regardless of any approach from north London.
Forest's business is not confined to defence. The club are also in talks over a move worth £13.6m including add-ons for Corinthians midfielder André, who only made his league debut for the Brazilian club a year ago but has quickly become one of the most talked-about young midfielders in the Brasileirão.
Corinthians are understood to be holding out for a higher fee, with the Sao Paulo club under financial pressure to raise funds but reluctant to sell their prospect below their valuation — reports in Brazil suggest Forest's improved offer stands at around €15m plus €5m in bonuses, after an initial €12m proposal was turned down.
The World Cup-winning Netherlands forward Memphis Depay, André's teammate at Corinthians, has previously described him as one of the biggest talents he has seen in his career, and Forest face competition from other European clubs, including AC Milan and Crystal Palace, who have also monitored the 20-year-old's progress this season.
The move would help fill the creative void left by Elliot Anderson's £116m departure to Manchester City earlier in the window.