A place in the group stages is up for grabs, and the Ghanaian outfit is set to host the 2007 African champions in the first leg of the first round at Kumasi's Baba Yara Sports Stadium.
"In football, everything is possible so Kotoko can win although the Tunisian team is stronger," Osei told Graphic Sports.
"The Kotoko players must be strong in terms of character, must be tactically disciplined and work extra hard in the game.
"If they exhibit these attitudes they will succeed."
Osei also has some concerns about the Porcupine Warriors.
"Kotoko have a new coach and have brought in some new players, so they are still working on tactical plans," he said.
"This will take time, so if the game becomes tough, the fans should still support them."