Carreras endured a season of diminishing returns last time out, managing just two goals and three assists in 38 appearances, form that convinced Real Madrid to move for Cucurella a few weeks ago and has already prompted the exit of Fran Garcia, who departed for pastures new with Ferland Mendy still on the books as a fourth option at left-back.
With that queue forming behind Cucurella, Carreras' immediate future in the Spanish capital looks anything but secure.
Chelsea have not forgotten about him. It was Xabi Alonso, now in charge at Stamford Bridge, who got the best out of Carreras during his own spell in the Real Madrid dugout last season, and that familiarity is understood to be a significant factor behind the club's renewed interest.
Alonso has not lost faith in a player he knows intimately, and with Chelsea still shopping for reinforcements before the window shuts, revisiting a deal for Carreras makes obvious sense to those running the club's recruitment.
Nothing is imminent, but the door has not been closed either. Real Madrid would need persuading to part with a player they only signed relatively recently, and Carreras himself has given no public indication that he wants out.
Still, with Cucurella now first choice and two more bodies ahead of him in the pecking order, growing frustration over game time this season would only add weight to any concrete offer Chelsea eventually put forward, particularly given Alonso's evident enthusiasm for reuniting with a player he trusts.
Carreras arrived at the Bernabeu from Benfica just a year ago in a deal worth around €50m, and looked an assured, near-automatic starter in his first months under Alonso before his form dipped and a reported dressing-room disagreement with Antonio Rudiger added to a difficult second half of the campaign.
Real Madrid, wary of taking a financial hit so soon after that investment, would likely resist any move that did not recoup close to what they paid, meaning Chelsea may need patience to turn renewed interest into an actual deal.