Manchester United have stepped up their interest in Monaco pair Kylian Mbappe and Tiemoue Bakayoko, having sent head scout Marcel Bout to assess the two players during the 3-1 Champions League victory over Manchester City on Wednesday, sources have told ESPN FC.
Real Madrid and Barcelona are also monitoring 18-year-old Mbappe, who opened the scoring in against City, while Pep Guardiola's City are admirers of defensive midfielder Bakayoko, whose late header secured Monaco's progress.
United manager Jose Mourinho has made attacking reinforcements a priority this summer with Wayne Rooney expected to leave Old Trafford, while a long-term successor for Michael Carrick is also being sought and Bakayoko, 22, had already been on his radar.
Bout, who arrived at United in the summer of 2014 as Louis van Gaal's chief opposition scout, remained at the club following the former Netherlands boss' dismissal at the end of last season and was given a more senior role by Mourinho within Old Trafford's scouting department.
He was in attendance at Stade Louis II on Wednesday as Leonardo Jardim's team overturned a 5-3 first-leg deficit to progress to the quarterfinals at City's expense, with sources telling ESPN FC that Mbappe and Bakayoko were the purpose of Bout's trip.
However, Monaco vice-president Vadim Vasilyev said on Wednesday night that the Ligue 1 club hope to hold on to Mbappe.
Mourinho has already told executive vice-chairman Ed Woodward of his priorities for summer recruitment, with Atletico Madrid forward Antoine Griezmann at the top of his wanted list.
Mbappe said after the match that Monaco's dominant first-half performance was the key to their success against City.
The French teenager struck after just eight minutes on Wednesday and he said in L'Equipe: "We really wanted to show them from the start that it wasn't going to be their day and that it would well and truly be ours.
"We managed to establish ourselves in their half of the pitch, we didn't let them play. Almost every chance was turned into a goal. I think it was a real blow to their morale when they went in 2-0 down at half-time. I don't think they expected that."
City hit back through Leroy Sane in the 71st minute to re-establish their aggregate lead, but Bakayoko headed home six minutes later to send Monaco through.
Portugal international Bernardo Silva said: "At 2-1, we didn't falter. That's what has been our strength this season, we're not afraid to play.
"Even at 3-2 in Manchester, we continued playing and that's also why we conceded five goals. But this evening, we're very happy. Thanks to Bakayoko for taking us into the quarterfinal."
He added: "It's a magical evening. If there is one very positive thing this season, it's that we have a group. When a player is missing, the replacements come into the team without us losing any quality. Now we'll see who we'll play against. There are only fantastic teams left. We dream of going beyond the quarterfinals."
ESPN FC's France correspondent, Ian Holyman, contributed to this report.