The Queens Park Rangers owner, Tony Fernandes, has said that he will leave the club if they are relegated from the Premier League this season. QPR suffered a humiliating defeat at home to Milton Keynes Dons in the FA Cup and are five points from safety at the bottom of the table.

The anger in the crowd – from those who remained until the bitter end, that is – was palpable and Fernandes, who bought the club in August 2011, is feeling the heat. Despite a vast expenditure on new players QPR have struggled and Harry Redknapp is the third manager they have employed since the takeover.

"Attendance was great," Fernandes said on Twitter. "Thanks to fans Everything worked. We will fix It. I'm still optimistic. Many fans attacking me. Doing our best.

"As I said we won't stop trying. As I have said many times I take all responsibility and will face the music. Always spirit up. If can't fix it I will be first to go."

Next up for QPR is the visit of Manchester City. "We will pick a different team on Tuesday," said Redknapp, who is hopeful Löic Rémy will be available after hamstring trouble.

Despite the mess at QPR this was undoubtedly the greatest day in MK Dons' short history. They had never reached the fifth round before and their veteran striker, Alan Smith, savoured every moment of a match in which they led 4-0 after 56 minutes. The 32-year-old was part of the Leeds side that reached the semi-finals of the Champions League in 2001 but said this victory rivalled that run.

"This one will be remembered as fondly as some of those results," Smith said. "Obviously it was not as spectacular as who you were playing against – they were all European giants. But it is a Premier League team who have spent a lot of money and we came and played good football. It is not as though we were backs to the wall. It proved how good we can be.

"It is one of the best results of my career. For a League One team to come to a Premier League team and be 4-0 up with 25 minutes to go … It was a strong QPR team as well. It was not as though they put young lads out as well or part of the reserve team – there were international players out there."

Smith is the same age as his manager but, while his career is drawing to a close, Karl Robinson's is in its infancy. The manager turned down an approach from Blackpool earlier this month and Smith believes he can go as far as he wants in the game.

"He plays a style of football that is very attractive to watch," Smith said. "People say we overplay and try to play too much for our division but everyone who comes to watch can see that everybody is confident on the ball and wants to play. We have brought some steel to the team and some characters and some winners – that is important.

"That is where Karl's coaching is first class. He has worked under some great managers and is doing a great job. Fingers crossed we can keep him because I am sure the vultures will be circling. It is difficult to keep a manager of that age and that quality."

Blackpool's offer was attractive but Robinson is trying to build something at MK Dons. Loyalty is important to him. "At this moment in time I'm in a good place personally," he said. "My family mean a lot to me. My dad had a heart attack last week and thankfully he's come over the back of that now. I think loyalty's a gift and I love the club that I work for and the group of players."

Man of the match Ryan Lowe (MK Dons)