There had been fears that Firpo, who has joined the club from Barcelona, would miss out on the chance to make his first outing for the club against the Red Devils, but the left-back has been passed fit following a knock.
Jamie Shackleton is also available following a head injury, but Diego Llorente is out with a leg complaint, meaning that Bielsa has a decision to make in the middle of his defence.
Robin Koch could ultimately get the nod alongside Liam Cooper, while Kalvin Phillips, who was excellent for England at Euro 2020, is expected to feature in the middle of the park.
Raphinha and Jack Harrison are likely to play as the wide players, with Patrick Bamford operating through the middle, while Stuart Dallas is a certain starter in central midfield.
Rodrigo Moreno's spot in the starting XI is far from secure, but there have been indications that Bielsa will select the Spaniard as part of a 4-5-1 formation on Saturday afternoon.
Tyler Roberts and Mateusz Klich are also options to feature alongside Dallas and Phillips, while Koch could potentially also play in midfield if Pascal Struijk is selected at the back.
Leeds possible starting lineup: Meslier; Ayling, Koch, Cooper, Firpo; Raphinha, Dallas, Rodrigo, Phillips, Harrison; Bamford