Scolari plans to move in January to try and lure Witsel to Stamford Bridge.
The Belgian international has already been watched on a regular basis by Arsenal boss Wenger's spies, and United were also present at the Sevilla match, along with at least another 25 scouts from England, Germany and Italy.
A source close to Liege said last night: "If Chelsea, or anyone else want to sign Witsel, they will have to pay what Everton paid for Fellaini. Liege do not need the money. The valuation would be at least £15m."