The Argentina defender directed criticism at technical director Jason Wilcox, arguing that United failed to strengthen sufficiently after securing a third-place finish in the Premier League last season and returning to Europe's premier club competition for the first time in three years.

United's latest loss extended their winless run to five matches, increasing the pressure on head coach Michael Carrick, who was appointed permanently in January after winning 12 of his 17 games as interim manager following Ruben Amorim's dismissal.

However, Martinez believes the scrutiny should extend beyond the dugout and the players, insisting that greater investment was needed to build a squad capable of competing against Europe's leading teams.

"I have to control myself a lot, but sometimes it's a reflection of the mirror of how our club is at the moment," he told Amazon Prime Video.

"We did a fantastic season last season and now we expect more from the top, more players to compete because many teams bring many players as well.

"Atletico have an amazing team and they deserved to win today. But I expect more (investment). 100 percent. I expect more from our technical director (Jason Wilcox)."

United invested around 155 million pounds in the recent transfer window, focusing heavily on midfield while leaving questions over their options at left-back and in attack, where Benjamin Sesko remains in need of additional support.

Martinez acknowledged that the players must also improve but stressed the importance of having sufficient depth to cope with demanding European fixtures.

"As players, we have to do more, but it is also important when you make a strong squad to be ready for this kind of night," he said.

The defender also rejected the idea that another managerial change would solve United's problems, pointing instead to the need for improvements elsewhere within the club.

"You can't keep changing, changing, changing the manager. What about other areas? I can't say more," he added.

Martinez argued that opponents have adapted to United's approach since last season, making further recruitment and tactical development essential if the club are to progress.

"He does his best," Martinez said of Carrick. "Every season is different. You can't stay with what you did last season.

"The teams know how you play, they know every detail. If you don't change, next season is a big problem."

Carrick declined to comment directly on Martinez's remarks, saying he had not seen the interview, but urged his squad to remain united despite their disappointing results.

"I haven't seen it. After a game like this you come here to try and get something from the game and you are disappointed and can be emotional," he said.

"We all care and show that in different ways, but now is the time to be together and work through."

Carrick maintained that the results had not reflected the players' commitment, adding that the squad had been determined to secure a positive outcome in Madrid.

Martinez's criticism comes amid uncertainty over his own future, with the defender having one year remaining on his United contract and no extension agreed.

Njabulo Blom impresses head coach Gavin Hunt on debut as Stellenbosch draw with Kaizer Chiefs