Brawn forced to miss Spanish GP
Technical director Bob Bell will take charge, with team chief executive Nick Fry and Mercedes motorsport vice-president Norbert Haug also at the Circuit de Catalunya.
A Mercedes spokeswoman said Brawn, whose team won last month's Chinese Grand Prix with Germany's Nico Rosberg for their first success as a works outfit since 1955, was expected to be back for Monaco later this month.
The team gave no details about the Briton's illness.
"Naturally we will miss him, be sure about this," seven-times world champion Michael Schumacher, who has worked with Brawn for nearly all of his record-breaking career, told reporters.
"But he will be in contact with us and support us in his maximum way. We (I) had to deal with his absence during some of the Ferrari days and will have to deal with it here this weekend," added the 43-year-old.
"But as you can imagine with all his experience and knowledge it is going to be certainly a challenge for us."
Brawn missed a few races while at Ferrari due to back problems and then took a year out of the sport altogether when Schumacher left Ferrari at the end of 2006 and began a retirement that lasted three years.
The team boss won multiple world championships with Benetton and Ferrari as a technical director and then led his Brawn GP to the 2009 title, after previous owners Honda had pulled out, before Mercedes then took it over.
Sunday's Spanish race is the fifth round of the season and first in Europe.