Hollmann, who had a spell with Zamalek's arch-rivals Ahli in the late 1990s, penned a one-year deal with the Egyptian Cup winners, the club said on their website.
He will earn 30,000 euros as a monthly salary, FilGoal.com understands.
The 59-year-old will replace Krol, who resigned at the end of last season due to personal reasons.
His first task will be to lead Zamalek in the highly anticipated clash against Ahli in the CAF Champions League on July 20th.
Both sides will meet again in the local Super Cup seven days later.
Hollmann led Ahli to two successive Egyptian League titles in 1996 and 1997, after which he started a 10-year bout with Gulf clubs.
Zamalek had been tracking Alberto Zaccheroni but they couldn't meet the Italian coach's financial requirements.