United's INEOS chiefs are standing firm on their valuation of the forward, who has enjoyed a resurgence in Catalonia with 10 goals and 13 assists in 34 appearances this season.
Barcelona's struggles in Rashford's absence - including a 4-0 defeat to Atletico Madrid and a 2-1 loss to Girona - may increase their urgency to secure him permanently, but United will not entertain any reduced offers.