Tusker failed to claim top spot in the league after another loss at the hands of Nzoia Sugar, a third consecutive 1-0 loss.
The Brewers have had difficulties failing to score in their last three league games.
This worrying form in the league has forced them to exit the SportPesa Shield Cup and concentrate on their chase of the Kenya premier league.
Club chairman Daniel Aduda confirmed thisysaying:
“It was not an easy decision to make but we want to help the team concentrate on the league. We have a target of winning the title and want to focus on that.”
The withdrawal from the cup means Tusker must now win the league to feature in the 2019/2020 CAF confederation cup.
The winner of the SportPesa Shield automatically qualfies for the CAF completion.
Tusker are currently fifth with 25 points in the league standings, seven points behind table toppers Bandari FC.
They will welcome AFC Leopards on Saturday at Kenyatta Stadium, Machakos.