The 17-year-old left winger is one of the brightest talents emerging at Sporting and is attracting interest.
But reports from Portugal today suggest a contract renewal is imminent after positive talks.
The new deal will run until 2025 and shield Joelson with a release clause of between €60m and €80m.
The clause is the only remaining sticking point between both sides, with Sporting wanting it set at €100m.
It will be another success for Sporting after renewing Eduardo Quaresma, Nuno Mendes and Tiago Tomas.
Called up by coach Ruben Amorim before the Coronavirus shutdown, Joelson has yet to make his first team debut.
However, the Portugal youth international will be a part of next season’s first team planning.
Arsenal will still hope to sign Joelson given their excellent relations with his agent Kia Joorabchian.
Any deal may have to wait another year or so, with Sporting determined to raise Joelson’s value before selling him.