Coach Antonio Conte desperately wants to add another full back to provide competition for Marcos Alonso.
Sandro has been his first choice since the summer, but Chelsea aren't prepared to spend £60m on the Brazil international, who is now a target for Paris Saint-Germain and Manchester United.
The club have also admired Porto's Alex Telles, but hope they can get Emerson for in the region of £20million.
He has only just returned from a serious knee ligament injury which he sustained last May and is behind former Manchester City defender Aleksandar Kolarov in the pecking order.
The highly rated 23-year-old has made just two appearances this season and Roma might be more willing to sell him than established stars Radja Nainggolan or Kevin Strootman.
Should Chelsea acquire a new left wing back, Kenedy will be allowed to join Newcastle on loan.