Slim will be assisted by compatriots Khalil Hassani and Jridi Faouzi as first and second assistant referees respectively. Nasrallah Jaouadi will be the fourth official.
The match is set to be played on Sunday, December 16, 2018, at the Kasarani Stadium, starting at 4 pm with the reverse leg slated for between December 21 and December 23, 2018.
The aggregate winner in this encounter makes it to the Group stage which comes with prize money worth Sh 56m.
Gor Mahia progressed to the next round after knocking out Malawian side Nyasa Big Bullets of Malawi in the preliminary round.