The Hoops boss is awaiting results from a specialist who has had a look at the Parkhead skipper's abductor problem although defender Mikael Lustig, who has a thigh complaint, has been ruled out of the trip to Turin.
Ahead of the Clydesdale Bank Premier League clash with Motherwell at Fir Park tomorrow, Lennon was asked if Brown would miss the trip to Italy, where the Scottish champions hope to overturn a 3-0 first-leg deficit, and both upcoming Scotland games.
"Oh yes, I would imagine so," he said.
"He (Brown) is out indefinitely.
"We are still waiting to hear from the specialist, whether he requires surgery or not and I am hoping that we will get a definitive answer by the end of the week.
"Lustig is still out and Charlie Mulgrew (glute), they are the only three absentees
"Lustig is out for two to three weeks, it is bone bruising so it could even be longer.
"So I imagine he will miss Juventus. We are hoping Charlie will be fit for Juventus and the game at the weekend.
"Kris (Commons) is back from his virus and Lassad (Nouioui) has had a bit of a virus but he is in the squad."
Meanwhile, Brown and defender Mikael Lustig will be missing again for Celtic's Clydesdale Bank Premier League game against Motherwell at Fir Park.
Brown has seen a specialist about his abductor problem and will discover on Monday if he requires surgery while Lustig is out with a thigh injury.
Defender Charlie Mulgrew is a doubt with a glute problem.
Provisional squad: Forster, Matthews, Wilson, Rogne, Mulgrew, Ambrose, Izaguirre, Forrest, Kayal, Ledley, Wanyama, Rogic, Stokes, Watt, Miku, Lassad, Zaluska, Samaras, McGeouch, Chalmers.