Alvaro Carreras left United for Benfica in 2024 before joining Real Madrid, where he shone in the El Clasico, defending well against Barcelona’s Lamine Yamal.
The defender looks to have a bright future at Madrid, which has only raised questions at United, who have struggled with Sergio Reguilon and Sofyan Amrabat at left-back not long ago.
Sadowski told Przeglad Sportow that United made a huge mistake in selling Carreras and says the sale exemplifies how the Red Devils are failing at youth development.
"He came to Manchester United when he was probably 16 (in 2020). A very hard-working and ambitious boy, he learned the language quickly - I know because I met him personally.
“Initially, his career path was quite good. He was loaned to Preston, received good reviews, and (then) United gave up on him, selling him to Benfica for a small fee.
"Carreras is a truly top-class player. There's a good chance he'll become the best, or one of the best, left-backs in the world. He scored a beautiful goal recently against Valencia in La Liga. It was a huge mistake for United to let him go. Something is missing here, and I think that something is United's lack of courage in investing in young players."
Last summer, United had a chance to repurchase Carreras, using their buy-back clause, but they chose to let the young Spaniard sign for Los Blancos instead, which will only frustrate fans even further.