The centre back has been linked with both Manchester clubs and Chelsea, with all three having sent scouts to watch him in action.
The France international is regarded as one of the most promising defenders in Europe, and is set to cost big money, with Porto demanding a fee of around £40m for his services.
Manchester United boss David Moyes is particularly keen to strengthen his defence in the summer, with Nemanja Vidic and Rio Ferdinand both set to depart at the end of the season.
Moyes has put the 23-year-old high on his wanted list of possible replacements, but Manuel Pellegrini is also keen to bolster his defence, and came close to completing a deal in January.
Meanwhile, Jose Mourinho is keeping close tabs on Mangala, who he views as a potential long term successor to John Terry.
But the trio of Premier League clubs are now facing a battle with Catalan giants Barcelona for his signature, with boss Gerard Martino registering his interest.
The Spanish champions are on the lookout for a long-term replacement for Carlos Puyol, who at 35 is expected to end his playing career within the next 12 months.
The news will come as a blow to the Premier League trio, particularly United who are looking increasingly unlikely to be unable to offer Champions League football next season.