The Sweden international has been in fine form this season, scoring 19 Premier League goals as Eddie Howe’s side look to qualify for the Champions League again.
Isak bagged a brace as Newcastle beat Nottingham Forest 4-2 on Sunday but was a surprise omission from the starting lineup at Anfield.
Newcastle have confirmed striker Alexander Isak will miss Wednesday's game against Liverpool with a “slight groin problem”.
Callum Wilson, who has suffered injury problems of his own this season, replaces the Sweden star in the starting lineup.
The club have confirmed that is because of a groin injury, though the severity of the issue was not fully disclosed.
