Guimaraes and Willock were both withdrawn in Monday's 2-0 defeat to West Ham United with respective glute and calf injuries and have emerged as doubts for this weekend's trip to the capital.
Both players could join Jamaal Lascelles, Sven Botman (both knee) and Emil Krafth (collarbone) in the treatment room, with those three all targeting a return in the New Year.
Dan Burn served a one-match suspension last time out, but he is available to return to Eddie Howe's starting lineup and will likely replace Lloyd Kelly at centre-back as Fabian Schar retains his spot in the heart of defence.
Kieran Trippier recovered from a thigh injury to feature as a substitute against West Ham and he will push to start on Saturday, although Valentino Livramento could once again be preferred at right-back as Lewis Hall continues at left-back.
If Guimaraes and Willock are not deemed fit to start, then Sandro Tonali could be recalled and Joelinton could drop back into midfield to link up with Sean Longstaff.
A potential role for Joelinton in midfield would open the door for either Harvey Barnes, Miguel Almiron or Callum Wilson to start in attack alongside Anthony Gordon and Alexander Isak.
Newcastle possible starting lineup: Pope; Livramento, Schar, Burn, Hall; Longstaff, Tonali, Joelinton; Gordon, Isak, Barnes