The Twitter account @Portu_Goal tweeted a picture of the official Benfica attendance sheet detailing the clubs who showed up to watch the big match in Liga Sagres.
The January transfer window may now be closed, but United and Liverpool are expected to be active in the summer and are getting a head-start on their close season business.
Similarly, Liverpool boss Brendan Rodgers was tipped to enter the market in January, but a late move for Yevhen Konoplyanka broke down and the Reds were left empty headed.
The Liverpool and United scouts were joined by a host of other top European clubs. With a wealth of talent on show, Monaco, Manchester City, Bayer Leverkusen and Everton among others had representatives in Portugal for the game.
Benfica won the top of the table match-up 2-0, although Sporting were not able to call upon highly rated United target William Carvalho.