Man United last week sent scouts to watch Sergej Milinkovic-Savic, with Jose Mourinho interested in signing the midfielder.
The Daily Mail report that United sent scouts to watch Savic against Salzburg, a game in which Lazio lost, ending their Europa League campaign.
The midfielder struggled and failed to make an impact in the defeat, something that may harm his chances of winning a move to Man United.
The 23-year-old has scored 11 goals this season and has been highly rated by Lazio. The Italian side have put a £89 million price tag on the midfielder.
United are also interested in Brazilian Fred, with United needing a midfielder in the Summer window with Michael Carrick retiring and Marouane Fellaini set to leave the club.
The Serbian is set to play in this Summer’s World Cup with Serbia, alongside Nemanja Matic. United fans will hope that Matic will be able to lure the midfielder to Old Trafford.