If the 24-year-old, on-loan from Bayern Munich, is unavailable Kovac is likely to start Poland under-21 international Radoslaw Majecki with last season's regular Benjamin Lecomte not registered for the competition.
"He has some stomach issues and doesn't feel too well," Kovac said at his eve of match press conference.
"We will see tomorrow," he added.
The Ukrainians, who finished third in their group last season despite beating Real Madrid twice, have a clean bill of health with Brazilian Pedrinho fit after being replaced in last week's third qualifying round second leg win over Genk after 37 minutes.
The Principality outfit are eyeing a first appearance in the Champions League since 2019 when they lost five of their six matches.