Midfielder picked up second red card of the season at a terrible time.
The 21-year-old was excellent off the bench against Birmingham City on Friday and could make a major impact for Leeds United at Craven Cottage.
Leeds United took a significant step towards securing a spot in the Championship play-off places with an impressive 3-1 victory over Birmingham.
The Whites beat Birmingham City 3-1 at St. Andrew's on Friday night.
Kalvin Phillips is in danger of falling out to the periphery of the squad, and Leeds United cannot afford to allow that to happen.
Leeds United fans have been voting on which young player has excited them the most so far this season.
The midfielder was sent off during the 4-3 loss against Sheffield United.
Alex Mowatt has joined Barnsley from Championship rivals Leeds United.
The emergence of Kalvin Phillips and Ronaldo Vieira has certainly eased the pain of Cook's absence.
The New Zealand striker felt sorry for his young team-mate.