Manchester United boss Sir Alex Ferguson says they do not make 'knee-jerk' signings.

Ferguson admits it can take two years to make an assessment on a transfer target.

"We've been planning for next season for a while," Ferguson said. "Our scouting goes on for the full season, sometimes two seasons when you monitor a younger player.

"You want to see how he does the next season.

"That is the process we go through. We've got some ideas where we're going and hopefully we can conclude them."