Scouts from Manchester United were reportedly in attendance to watch Sporting Lisbon's 1-0 win over Moreirense at the weekend.
According to A Bola, one player of interest was supposed long-term target William Carvalho.
The 24-year-old is primarily a holding midfielder, although he can also operate in the centre of defence.
The report adds that winger Joao Mario was also on United's radar.
Mario, 23, has found the net on six occasions from his 35 appearances in all competitions for Sporting this term.
Is has been suggested that both players are admired by Jose Mourinho, who is expected to take charge of the Red Devils in the summer.
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