The 22-year-old has a release clause in his contract which has been set at €50million (£42.4m).
Any interested parties have been informed that they would need to match that fee in order for transfer talks to be opened.
Chelsea are reluctant to dig that deep and are understood to have shelved their interest.
Jose Mourinho had reportedly been looking at Mangala as a possible addition to his defensive unit.
It remains unclear how prominently John Terry will figure in his plans next season, while question marks have been raised as to David Luiz's long-term future at Stamford Bridge.
France international Mangala was reportedly considered to be a useful centre-half option for the present and future, having impressed since swapping life in Belgium at Standard Liege for that at Porto in 2011.
His current employers have no plans to let another top talent slip through their grasp, though, and will make potential suitors spend big if they decide to follow up their interest.
Porto president Pinto Da Costa said in A Bola: "This footballer only leaves our club if someone pays the release clause."