Sir Alex Ferguson's side are expected to complete the formalities of an alliance with Sporting in the coming months, with Carlos Queiroz involved in the negotiations, and the Portuguese press claim United will bid to bring the talented Under-21 internationals to Manchester.
However, Charlton have been most active in the scouting market in Portugal recently, as they were represented at both Porto's match with Moreirense, and the Under-21 clash with Greece.
Sporting starlets Ronaldo and Quaresma (pictured) led the Greek defence a merry dance on Tuesday, and apparently had scouts drooling, not only from Charlton, but also Celta Vigo, Chievo, Lens, Parma and Feyenoord.
The exact identity of Charlton's target is not yet known - no player was involved in both the domestic and international game - but former loanee Jorge Costa did feature for Porto at the heart of their defence.
However, it would seem unlikely that Alan Curbishley would bring the experienced centre half back to The Valley.
