Manchester United boss Sir Alex Ferguson is tracking Benfica midfielder Axel Witsel.

The Times says \Ferguson was scheduled to watch Axel Witsel play for Benfica against Chelsea in the Champions League quarter-final, first-leg this week.

The Manchester United manager has been tracking the Belgium midfielder, 23, who is value at in excess of £20million and signed a five-year contract when he moved from Standard Liege in July. He received death threats after he broke Marcin Wasilewski's leg by stamping on the Pole's ankle during the match between Anderlecht and Liege in 2009.