Manchester United scouts were posted to watch Porto pair Diogo Costa and David Carmo.
A Bola says United manager Erik ten Hag sent scouts to watch Costa and Carmo on Friday in Porto's 4-1 win against Braga with the former viewed as a replacement for David de Gea.
The 23-year-old Costa – who has been capped seven times by the Portuguese national team – and his teammate David Carmo, a central defender, are both on United's radar. Both have attracted long-term admiration from United and that interest has been stepped up since Ten Hag's appointment.
Carmo was signed by Porto from Braga this summer but has attained glowing reports from United's scouts, although they currently do not view central defence as a priority position following the arrival of Lisandro Martinez this summer. However, with long-term doubts over the future of Harry Maguire, Phil Jones and Axel Tuanzebe, it is likely that Carmo's progress will continue to be monitored.