Barca first made contact with Aarons' agents over a transfer in May and have already agreed on personal terms with the right-back.
However, they have been unable to strike a deal with Norwich, with an initial offer to take Aarons on loan with an option to buy next summer for around €20 million knocked back by the Championship club.
A second offer has also been turned down but sources told ESPN that Barca haven't completely given up hope of landing the England under-21 international yet after making him their No.1 full-back target.
Sources at the Catalan club have told ESPN that Semedo could leave in the next week, with talks at an advanced stage with a Premier League side.
Barca hope to sell Semedo for over €30m. They plan to re-invest that money on a younger right-back to compete with Sergi Roberto this season.
Aarons, 20, has emerged as their preferred option but they are also managing a number of alternatives in case they are unable to find a breakthrough in negotiations with Norwich.
Barca could still push ahead with signing a full-back even if Semedo stays. However, they cannot buy until they offload players, which is why they initially proposed a season-long loan when negotiating for Aarons.