Jose Mourinho has identified either Radja Nainggolan or Saul Niguez to replace Michael Carrick at the end of the season.
The Red Devils boss is keen to replace the ageing 36-year-old who is believed to hang up his boots at Old Trafford next year.
According to the Daily Star, two scouts were sent to watch the Roma star and Atletico Madrid ace respectively when they came up against each other in the Champions League.
Both midfielders were in action at the Stadio Olimpico in the 0-0 draw in Italy, as Mourinho is already planning to bolster his side next summer.
Nainggolan, 29, is seven years older than the Spanish maestro, and recently penned a new deal with the Serie A side until 2021.
The Belgian snubbed an approach from United in the latest transfer window, citing he is happy in Rome.
While Saul put pen to paper back in July as he agreed an astonishing nine-year contract extension with Diego Simeone’s men until 2026.
And it was revealed back in June that the Europa League winners turned down the chance to sign the 22-year-old three years ago – a decision they will be surely ruing.
Carrick – the current skipper at United – is yet to feature this season after the signing of Nemanja Matic from Chelsea.
However he could be set to get some game time with Paul Pogba rumoured to be out of action for up to 12 weeks.
The ex-Tottenham man has made 459 appearances for United since joining in 2006, and made 38 appearances last campaign under Mourinho.