Last Updated: Wed, 02 Apr 2014 16:46
Manchester City are being linked with moves for Inigo Martinez and Alen Halilovic while Napoli could lure Martin Demichelis away.
City and United are both contenders to sign 22-year-old Real Sociedad centre back Martinez who is left-footed and would be an ideal foil for Vincent Kompany.
United are looking to replace Nemanja Vidic and are also in the running to sign Porto centre back Eliaquim Mangala - but he is likely to cost many million more with City having long-admired the French international.
City could benefit from the international transfer ban that has been slapped on Barcelona with teenage midfielder Halilovic not yet having completed his proposed switch from Dinamo Zagreb.
Barca beat a number of rivals to the 17-year-old starlet when they announced an agreement last month, but he will be unable to move to the Nou Camp unless they win an appeal against the ruling.
Demichelis, 33, could be on his way out of the Etihad at the end of the season with Napoli now said to be interested in his signature.
The former Bayern Munich defender is unlikely to hang around next season if City sign a top class centre back to go alongside Kompany.
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