Lehmann is keen to see Milan keeper Mike Maignan live.
He told La Gazzetta dello Sport: "Maignan is strong, but I want to see him live to understand if he is among the top 5 in the world.
"(Gregor) Kobel is good, but he is still 25 years old and still young."
Lehmann added: "I see two teams with the same possibilities. Of course, the Gialloroneri play at home and that may be a factor."