Sunderland’s recruitment team are understood to have agreed the framework of a deal worth around £21.5m with their counterparts at Stamford Bridge and are trying to engineer a swift resolution to the ongoing discussions.
However, they are not the only club to have held talks with Chelsea over the Serbia international, who spent last season playing in the French top-flight with Strasbourg, where he was a team-mate of Diarra.
Bournemouth are also understood to have held advanced discussions as they look to sign a replacement for Kepa Arrizabalaga, who spent last season on loan at the Vitality Stadium, but who completed a permanent move to Arsenal from Chelsea earlier this week.
Bournemouth have discussed financial terms of their own with the Chelsea hierarchy, with two continental clubs also believed to be involved ongoing talks over Petrovic.
Sunderland officials are aware of the competition, hence their desire to hold personal talks with Petrovic and his representatives as quickly as possible. Ideally, Sunderland would like to have the situation resolved before the end of the weekend.