Manchester United boss Sir Alex Ferguson has urged fans to be the "12th man" ahead of Wednesday's Champions League semifinal against Barcelona.

"There have been so many occasions over the years, we've always referred to it time and time again, of the crowd being the 12th man in the way they create such great encouragement," the boss told MUTV.

"If it's like that on that night with our supporters bringing their red and white scarves it should be fantastic. We want to make sure it's a real sea of red and white, and if we can do that we have a big, big chance [of reaching the final]."