The Argentine defender questioned United's ambition after Tuesday's loss in Spain, saying he had expected greater investment in the squad following their third-place Premier League finish last season.

Martinez also took aim at technical director Jason Wilcox, insisting he had expected the club to do more in the transfer market as United prepared for their return to Europe's top competition.

United signed three midfielders - Carlos Baleba, Youri Tielemans and Andrey Santos - for around 150 million pounds, but their spending was significantly lower than that of several Premier League rivals.

However, Martinez has now attempted to clarify his comments, acknowledging that his emotions got the better of him after another disappointing result.

"After the match, I spoke out of anger and frustration at not getting the result we all wanted," he wrote on social media.

Martinez insisted his call for greater investment was about maintaining the standards expected at Manchester United and ensuring the club has the resources to compete at the highest level.

"When I talk about wanting more, I'm talking about the ambition we must all have as part of this club. To keep growing, to become stronger and to have everything we need to compete at the highest level," he added.

"These are standards we must all hold ourselves to, starting with me."

The defender also reaffirmed his support for his teammates and manager Michael Carrick, stressing that unity and hard work were essential if United were to turn their season around.

"I believe in my teammates, our manager and everyone working to help this club move forward. I'm convinced that the way forward is to keep working together, with ambition and commitment," Martinez said.

United's struggles have placed the squad under increasing scrutiny, with Martinez himself facing criticism for his performances. He scored an own goal in the 1-1 draw against Fulham last month and was outmuscled by Dominic Solanke as 10-man Tottenham salvaged a point at Old Trafford last weekend.

United are also enduring their worst start to a Premier League season in 40 years, increasing the pressure on Carrick just months after he was appointed permanent manager.

Carrick's side face another major test when they travel to historic rivals Leeds on Sunday in the Premier League.

Real Madrid boss Carlo Ancelotti rules out any more signings