Portuguese newspaper A Bola estimates that Manchester United scouts watched Sporting Lisbon midfielder William for a 12th time on Saturday.
Sporting Lisbon beat Olhanense 1-0 thanks to an early goal from Carlos Mane, with Manchester United target William anchoring the midfield.
David Moyes is keen to get as much information on William before Manchester United launch a summer bid with A Bola claiming the reports the Scot has received being largely positive.
As of yet, Manchester United have not made an official move for William.
The 21-year-old midfielder is contracted to Sporting Lisbon until 2018 and has a release clause worth 45 million euros.
Manchester United have had great success in the past buying players from Sporting Lisbon, for example Cristiano Ronaldo.