The presence of Manchester United scouts at Porto’s 3-0 win over Maritimo have stoked rumours that David Moyes is lining up a bid for defender Eliaquim Mangala.
The 22-year-old centre-half was also watched by representatives from Barcelona, while Chelsea and Paris Saint-Germain have been credited with an interest in the player during the summer.
Mangala signed for the Portuguese champions from Standard Liege two years ago for a fee in the region of £5.5m, but with so many top clubs vying for his signature, Porto could expect to receive at least three times that amount were they to sell.
During his first full season as a regular starter at the Estadio do Dragao, Mangala starred in a Porto defence that conceded just 14 times in the league.
He also helped himself to four goals in his 23 league appearances as Porto pipped Benfica to the Primeira Liga title by a single point.
Moyes – whose United side are now 3/1 third-favourites for the title behind Manchester City and Chelsea following their goalless draw with the Stamford Bridge club – is keen to put his personal stamp on the team he inherited at the start of July, having failed to make a signing so far.
They have their first-choice centre-half pairing back now that captain Nemanja Vidic – who was ruled out for most of last season – is fit and playing alongside Old Trafford stalwart Rio Ferdinand.
However, both players are the wrong side of 30 and concerns over recurring injury problems, particularly in Vidic’s case, have led manager Moyes to seek extra cover.
Reserve centre-halves Chris Smalling and Phil Jones have been asked to play at right-back, following an injury to Rafael, and in central midfield respectively, leaving Jonny Evans as the only other senior stopper at Old Trafford.
United were thought to be interested in Benfica’s Argentina international Ezequiel Garay, but are unwilling to pay the £20m plus fee demanded by the Lisbon club.