Barcelona are the biggest threat to Manchester United's hopes of retaining their Champions League crown, claims Reds boss Sir Alex Ferguson. "Barcelona are the form team, they have been terrific this season and everyone is taking notice of them," he said.

"Their first-half performance against Lyon in the second leg of the first knock-out round (which they won 5-2 at the Nou Camp) was absolutely brilliant - they were four up in no time.

"They can be a threat to anybody and are quite rightly one of the favourites. The English teams have proven the strength of the Premier League in recent years.

"Last season we had three in the semi-finals and two in the final, the previous year there were three in the semis and Liverpool made it to the final.

"But we have to recognise that our threats don't just come from England, the big one will come from Barcelona."

"I'm not sure they have improved a lot from when we played them last season but they have had a better defensive record since Guardiola took over as coach last year," Ferguson told Inside United.

"There has maybe been a bit more concentration on defending than there had been in previous times. That's not a criticism of Frank Rijkaard, I just think Guardiola has brought in the awareness that defending is just as important as attacking.

"Gerard Pique, for instance, left us to go back there and has done really well for them. We always knew of his abilities - good talent, mobility and a winning mentality - so I think he's improved them.

"They got off to a great start to the season and it wasn't until January that they hit a blip and that happens to everyone. They're over that now, so they'll be the threat."