Manchester United defender Lisandro Martinez says he "spoke out of anger and frustration" when launching a scathing attack on the club's hierarchy.

The Argentina international criticised United for not strengthening the squad in the summer following qualification for the Champions League in comments made after the 2-0 defeat at Atletico Madrid in the Champions League group phase on Tuesday.

Martinez said he expected more investment in the United squad and "more from our technical director [Jason Wilcox]".

However, while he stopped short of an apology, he said he has "belief in my team-mates, our manager [Michael Carrick] and everyone working to help this club move forward".

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

"Those who know me know how I live football, with passion, commitment and a huge desire to win. And when things don't go our way, it hurts, especially when representing a club with the history and stature of Manchester United.

"My words reflect how I feel and how much I want to see this club competing for the biggest honours.

"Those high standards are part of how I see football and the responsibility that comes with wearing this shirt.

"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.

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

Manchester United have not won in five games since beating Sabah in the Champions League on 10 September.

They have won just two of their nine games this season and are 13th in the Premier League with six points from as many games.

Martinez's contract expires at the end of the season and United have the option to extend it by another year.

He added: "I know that, first and foremost, it's us, the players, who have to deliver, and I put myself at the front of that responsibility.

"We need to demand even more of ourselves and work together to take Manchester United back to the top.

"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.

"My goal has been the same since day one, to win, compete at the highest level and to give everything I have for this badge."

Manchester United's next game will be at Leeds United in the Premier League on Sunday, 18 October.