The 26-year-old Argentina forward injured his thigh in a 2-0 Primera Division win over Almeria on Saturday and has been ruled out for between two and three weeks.
Hoops boss Lennon, whose side lost their Champions League Group H opener 2-0 to AC Milan at San Siro, said: "It is obviously very good news for us because he is the best player in the world.
"However, it is tinged with sadness because it is always fantastic to see the great players play here in Glasgow.
"We are looking forward to the game, we welcome Barcelona with open arms and we are hoping it is going to be another great occasion."
Neymar is likely to take over Messi's superstar mantle for the evening and become the focus of the Barca attack but Lennon does not believe the two players can be compared.
The former Parkhead skipper said: "It is like comparing a dog with a cat.
"They are two different types, two different players altogether.
"He (Neymar) is wonderfully gifted, quick, predominantly playing on the left-hand side and he has goals in him.
"He is only young and he has a fantastic future but it is far too early to make comparisons to Messi.
"There is only one player currently who could arguably be around the calibre of Messi and that is Cristiano Ronaldo."