08/27/2014 10:06 EDT | Updated 10/27/2014 05:59 EDT

Manchester United, Van Gaal facing serious questions after humiliating exit in League Cup

MANCHESTER, England - Louis van Gaal has always said it could get worse before it gets better at Manchester United.

He couldn't have thought it would get this bad.

Barely two months ago, a jubilant Van Gaal was leaping out of his seat and high-fiving his Netherlands players as he masterminded a 5-1 thrashing of Spain at the World Cup in Brazil.

Compare that to the glum, stony-faced figure of Van Gaal who remained glued to his seat during United's humiliating 4-0 loss to third-tier club MK Dons in the second round of the League Cup on Tuesday.

To the right of him, Ryan Giggs — a club great who is now Van Gaal's assistant coach — buried his face in his hands.

Even though United fielded a virtual reserve team, albeit one containing established internationals like Javier Hernandez, Danny Welbeck and Shinji Kagawa, it was one of the most embarrassing results in the history of England's biggest club.

Following on from a winless start in the Premier League after two games of Van Gaal's tenure, serious doubts are already being raised about the Dutchman's use of the 3-5-2 formation and the lack of depth in his squad, especially in defence.

"The process needs time," Van Gaal said. "We know exactly what we are doing."

Time is something United doesn't have.

David Moyes only lasted 10 months last season before being fired, and Van Gaal has already virtually written off United's chances of winning the Premier League in this second straight year of transition at Old Trafford.

With no European football this season, the FA Cup remains the only genuine opportunity for silverware — and it is still only August.

The optimism of pre-season, when United won six straight games under Van Gaal, including victories over Real Madrid and Liverpool, has disappeared.

Van Gaal is now left hoping a spending spree of about 130 million pounds ($215 million), capped by the club-record signing of Angel Di Maria for $99 million hours before the MK Dons game, pays off.

Van Gaal has played three at the back in his time at United but his defenders look uncomfortable in that formation and the wing backs — so crucial in a 3-5-2 — utilized by the Dutchman have no experience in that position.

Di Maria's arrival will not just introduce pace and fresh ideas into the team's midfield, it might also mean United changing tactics.

"We shall see if with Di Maria we have to change the system or not," Van Gaal said Tuesday.

With less than a week before the transfer window shuts, the loss again highlighted the need for defensive reinforcements. Left back Luke Shaw and left-sided defender Marcos Rojo have joined but United appears to still require an experienced centre back.

The defending was awful against MK Dons, with Jonny Evans — a regular in recent seasons — to blame for the first goal.

Van Gaal didn't escape blame, either, with critics questioning why he felt the need to rest star players like Wayne Rooney, Robin van Persie and Juan Mata when United isn't in Europe this season.

Even with a weakened side, how could a club that won the Premier League 15 months ago and was playing in the Champions League final three years ago play so poorly against third-tier opposition that didn't even exist a decade ago?

On Twitter, Manchester City striker Edin Dzeko tweeted "Hahahaha" after MK Dons' second goal went in.

With only the league to concentrate on until January, the loss may boost United's chances of getting back in the top four and returning to the Champions League.

For the time being, though, the embarrassment remains acute.

"I am not shocked because I know what can happen," Van Gaal said. "A new team is not built in one month.

"It's difficult for the fans, I know that, but they have to believe in our philosophy," Van Gaal added. "At the end, they can judge."