When the draw was made for the Champions League quarter-finals, the smart money said that Manchester United was the best placed of four Premier League representatives to make it to the semi-finals.

Events in Spain and Old Trafford last night have turned that situation on its head and right now, Arsenal are sitting pretty while Alex Ferguson frets.

Manchester United are now in a treacherous position and if I was a betting man, I'd be putting my money on Porto to win through to the semi-final.

It never ceases to amaze me how mercilessly football exposes weaknesses. Over time, if there's something wrong at a football club, it will show.

IDENTIFY

Often, it's difficult to identify exactly what is wrong and right now, that's true of Manchester United -- both outside and inside the camp.

From the outside looking in, it looks as if there's a range of problems that could be having an impact though without the knowledge you get from being centrally involved, no observer can ever be sure.

Obviously enough, those within the club will have a better handle on the ebb and flow behind the scenes but sometimes, even those closest to the action are as baffled as everyone else when a slump happens.

Alex Ferguson probably thought that Sunday's last-gasp and hugely dramatic win over Aston Villa would help his players turn a corner but we saw last night against a better than decent Porto side that the opposite has happened.

He's an optimist by nature and I'm sure he saw poor results against Fulham and Liverpool and poor performances over both legs against Inter Milan in the Champions League as nothing more than a blip after a long run of clean sheets.

But it's definitely more than a blip and that tells me that Ferguson himself is unsure about what is wrong with his team. That has to be a big worry for Manchester United fans if it's true.

Against Porto, Manchester United were a mess. Dreadful at the back, loose in midfield and apart from Wayne Rooney, lacking utterly in the type of urgency you would expect in the quarter-final of the Champions League.

The competitive instinct and ruthless efficiency that drew in Liverpool over a 14-game run and eventually left Rafa Benitez trailing behind has evaporated completely and this will worry Ferguson more than anything else.

I have no doubt that the hype that grew out of that winning run found its way into the heads of everyone at Old Trafford and that complacency, in some form, has had a say in the steady decline in performance levels -- particularly at the back. It's hard to understand how Nemanja Vidic, one of the best defenders in world football for the last few seasons, suddenly looks like a weak link, but he does.

Johnny Evans looks like what he is -- a young man who should be finding his feet at the very highest level forced by injury and suspensions to play game after game.

STRESSES

Physically, the number of games Manchester United have been playing shouldn't be a big issue but for a young lad like Evans, the mental stresses and strains have clearly taken a toll.

Under normal circumstances, Ferguson would have rested Evans but he cannot afford that luxury in these circumstances.

Nor can he, at this stage, afford the indulgence he has granted Ronaldo, a player who is a shadow of what he was last season and might as well have been in Madrid last night for all the good he did his team.

As I've said before, I can only speculate about Ronaldo's impact in the Manchester United dressing room but it seems to me that players like Rooney, Paul Scholes, Ryan Giggs and Gary Neville -- honest lads with the right attitude -- cannot be happy with the effort he makes and the way he behaves on the pitch.

Time and time again he was shown up by Rooney and then Tevez who did not feel it beneath them to chase back to help what was clearly a very jittery back four.

He set the tone for this early on when he lost possession and watched from a distance while Porto went a goal up.

He lost the ball a lot after that as well.

When Ronaldo is playing well and Manchester United are winning, it's easy for his team-mates to overlook the histrionics and petulance, especially if he's scoring a hatful of goals.

But at a time when the pressure is building to a peak and you need everyone pulling in the one direction, they must see that Ronaldo is not playing with the same commitment and drive he had in his game last season and wonder why not?

Should Ferguson drop him? I would if I had someone like Tevez on the bench who will give you everything he's got and goals as well.

Will Ferguson drop him? Almost certainly not. He is wedded to Ronaldo for good or ill and that was the case once he chose to fight to keep him instead of cashing his chips as he did with David Beckham.