WATCH: Paul Merson and Charlie Nicholas debate Arsenal's defensive problems

Paul Merson and Charlie Nicholas had a heated debate about how to solve Arsenal's defensive problems on Soccer Saturday.

Arsenal were knocked out of the FA Cup with a 3-1 defeat at home to Manchester United on Friday night.

But is boss Unai Emery to blame for their poor defending? Or do they simply not have the quality in their squad to cope against top attacks?

Watch the video above to see former Arsenal players Merson and Nicholas debate the issue or read on to see what they had to say…

Charlie Nicholas: "The only thing that changed was the period of 20 unbeaten and that gave some people hope that there was a big swing coming. I still think they're good going forward - but they always were under Arsene Wenger.

"But I go back to what I said a couple of weeks ago. It's been brewing there for four or five seasons. Even when Arsene spent a lot of money on defenders, it was the wrong defenders. Now the crowd know it and there's nothing the owners can do, they're not prepared to do anything to help this manager.

"If you don't help the manager strengthen where you're weak, what do you expect to change? I've given up on Arsenal this season because even though they can beat Spurs and Chelsea, they are a mess at the back.

I've given up on Arsenal this season because even though they can beat Spurs and Chelsea, they are a mess at the back.

"It got to the stage on Friday night, when (Shkodran) Mustafi was warming up, you could hear the whole stadium saying 'really, will this make any difference?' It doesn't make any difference whether they're injured or they're fit, at the back they don't know how to defend. Sadly, even Petr Cech, as great as he's been, you could see last night, the reason why he wants to finish now."

Paul Merson: "When (Mesut) Ozil comes on, I sit there and think 'how's he not playing?' I know people say, 'he doesn't run around, he doesn't track back', but none of them track back. The two holding midfield players were nowhere to be seen in the first half for the goal, when (Romelu) Lukaku broke away the two holding players were nowhere to be seen. The young right-back, didn't bother to track back for (Jesse) Lingard's goal.

"I think the manager is getting away with it at the moment. I like the manager but it's like, 'you know what, everybody knows we're bad at the back, so we'll just play this way. It don't matter, it ain't me. These aren't my defenders. We were a mess before'. Set up a certain way!

He is an experienced manager who has won the Europa enough times to be tactically aware. Solskjaer left Emery standing yesterday.

"Will Ole Gunnar Solskjaer get the Manchester United job? I'm not sure. But he out-tacticed Emery yesterday. This is an experienced manager who has won the Europa enough times to be tactically aware. Solskjaer left Emery standing yesterday. Fair play to Solskjaer, give credit where credit is due, yesterday he was very tactically aware."

Charlie Nicholas: "I don't know what we expect from Arsenal. You talk about tactics. Yeah, he can set up a bit more defensively and be a bit more shrewd but this defence - and I mean all the defence - is a shambles.

"He's tried a back five, he tried a back four last week that beats Chelsea. He tried another back four last night. It's a shambles again. It's a mess. The whole defensive set-up is a joke. From right-back, centre-backs, if it's two or three, to left-back. There's not a defender in the club. It's shameful that it's allowed to go on like this.

"I get where you're coming from, and the manager must take his responsibility but these players are a million miles from being good enough. He has to get rid of them all defensively. Out of eight defenders he keeps two, if you're lucky."

Paul Merson: "Just get four at the back and say, you four stay there, you two sit in front."

Charlie Nicholas: "What four are you going to pick then?"

Paul Merson: "Whoever they are, four defenders."

Charlie Nicholas: "They've been a shambles for the last three, four years."

Paul Merson: "Four at the back, two in front…"

Charlie Nicholas: "They tried that!"

Paul Merson: "Well, try it again! Don't just say, 'oh we're not going to do it!'

"There's got to be something wrong with the manager. They've got four unbelievably talented forwards, whoever they are, go and play. The other six, sit back, stay tight, get on with the game!"