Nicolas Otamendi
Otamendi will reportedly join Chelsea next summer. (Reuters)

Chelsea have agreed a deal to sign Porto defender Nicolas Otamendi at the end of the season having fended off interest from Atletico Madrid and Juventus, reports suggest.

The powerful centre half has become an integral part of Porto's defence following his arrival on Europe from Velez Sarsfield in 2010 but appeared to be on the brink of a move to Atletico on a number of occasions during the summer transfer window.

Porto resisted such attempts but Portuguese publication O Jogo and Marca now suggest the club are now resigned to losing the 25-year-old to Chelsea.

The Blues had reportedly made Otamendi's defensive partner Eliaquim Mangala their top defensive target during the summer months but were strongly told by Porto that only an offer of €50m - the Frenchman's release clause - would be enough to convince the Portuguese champions of letting their man go.

Consequently, Jose Mourinho has now turned his attention to Otamendi and the club are believed to have struck a deal with Porto that will see the defender, who has a release clause of €30m written into his contract, arrive at Stamford Bridge in time for the 2014/15 season.

Although the club will be expected to pay the Argentine's release clause, it may be seen as the necessary price of doing business given their current options in defence. Although John Terry has enjoyed a resurgent season under Mourinho, the club will be wary of finding a replacement for the 32-year-old sooner rather than later.

The long term role of David Luiz under the former Real Madrid manager's tenure remains uncertain while Branislav Ivanovic would appear to be a preferred choice at right back.

Otamendi's reportedly close move to Atletico was speculated upon when Porto and the in-form Spainards met in the Champions League this week. But when quizzed on the possibility of a January move to the Vicente Calderon, the defender was dismissive.

"I'm at a great club, playing in the Champions League, and there's nothing up with Atletico Madrid, those are just rumours," Otamendi was quoted as saying by TMW.

"I'm willing to keep fighting for the Porto shirt, and give me best to gain new successes."