The 44-year-old replaced Nikolay Mitov, who was sacked after Levski were knocked out of Europe's second-tier club competition by unfancied Kazakhstan side Irtysh Pavlodar 2-0 on aggregate last week.
However, Jokanovic will not be able to take over in time for Levski's first league match of the season on July 21.
"He'll travel to Serbia and Madrid and he'll to return to watch the Botev (Plovdiv) match on Sunday and sign the contract," Sirakov said. "Assistant coaches will take charge in the game."
Levski were lambasted by local media after their Europa League exit which fans called "the most shameful failure in the club's history".
Supporters of the 26-times Bulgarian champions announced they would boycott the game at Botev.
Jokanovic, capped 64 times by Yugoslavia between 1991 and 2002, was named as Partizan Belgrade's coach without any coaching experience in 2007 and led the club to two successive domestic doubles.
"I know little about Levski and I want to see the players first," said Jokanovic. "I know that the team have not won anything for four years and need to get stronger."
Last season, Jokanovic, who also played for several Spanish teams, led Muangthong United to their third league title in Thailand.