Italian journalist Nicolo Schira says Blues transfer chief Marina Granovskaia is working on the deal to bring Oblak to London.
He tweeted: "Chelsea could buy a new goalkeeper this summer.
"Blues are not satisfied of Kepa, who could leave and come back to Spain. The first choice of Lampard is Jan Oblak.
"Talks opened with agent of Atletico Madrid's GK. The transfer is not simple, but Marina Granovskaia in action."