The 22-year-old Spaniard, who rejoined his boyhood club this summer, has quickly made his mark, leaving United to regret not giving him a proper shot under former manager Erik ten Hag.

Both United and Real Madrid, giants of world football, were busy in the summer 2025 transfer window. United bolstered their squad with Diego Leon, Matheus Cunha, Bryan Mbeumo, and Benjamin Sesko, aiming for a top-four Premier League finish.

Meanwhile, Real Madrid, now led by Xabi Alonso, brought in Dean Huijsen, Trent Alexander-Arnold, Franco Mastantuono, and Carreras to chase La Liga and Champions League glory.

Carreras, who left Real Madrid's youth setup for United in 2020 seeking first-team opportunities, never broke through at Old Trafford. Despite impressing in United's youth teams and during loan spells at Preston North End, Granada, and Benfica, Ten Hag didn't see him as ready for senior action.

In 2024, United sold him to Benfica for 6 million euros, securing a 15 percent sell-on clause and a buy-back option.

Real Madrid pounced this summer, signing Carreras for 50 million euros. He made an instant impact, playing 62 minutes in a pre-season friendly against WSG Tirol.

Spanish outlet Defensa Central reported United's regret, with a headline claiming, "Manchester United in turmoil over gifting Carreras to Real Madrid." The report highlighted that United's failure to trigger their buy-back clause has left "important Red Devils figures" second-guessing their decision.

The criticism isn't limited to Spain. The Manchester Evening News, on July 16, called Ten Hag's choice to overlook Carreras "inexplicable," noting he never made a senior debut despite being named in four Premier League squads under interim boss Ralf Rangnick. Instead, United loaned in Tottenham's Sergio Reguilon while sending Carreras to Granada on the same day, September 1, 2023.

Carreras didn't hide his frustration. In a December 2023 interview with The Athletic, he said, "United gave me the message that I should go out on loan, that Ten Hag didn't count on me, that I should gain experience. But football doesn't end at one club. My goal was to return to United and earn a place."

His ambition to shine at United never materialized, but his move to Real Madrid has him on a bigger stage.

At his Real Madrid unveiling on August 6, Carreras expressed gratitude to Benfica, saying, "They gave me an opportunity. All my teammates, the fans, everyone treated me well. I'm forever grateful". Notably, he avoided mentioning United, a sign of lingering disappointment.

He added, "I'm very happy. I can't wait to play at the Bernabeu. We have to work together to win all titles".

United's loss is Real Madrid's gain. While Carreras flourishes, United are banking on young left-backs Patrick Dorgu, signed from Lecce in 2024, and 18-year-old Diego Leon, who joined Ruben Amorim's squad this summer.

However, with Carreras now starring for one of Europe's elite, United's decision to let him go looks like a costly misstep.

Alvaro Carreras shines at Real Madrid as Man Utd rue missed chance