"It looks like anything up to about eight to 10 weeks," said Lennon of Wilson's lay-off.
"He has a tear in his Achilles tendon.
"He had the scan yesterday and the specialist said he would have to be out as long as that.
"It is a huge blow. We already have Emilio Izaguirre and Cha Du-ri out for a few weeks. It just means we have to re-jig things a little bit in defence.
"On the plus side Charlie Mulgrew has served his suspension and he will be back in contention for both games this week and he makes us better.”
Lennon admits he will be dipping back into the transfer market once the window re-opens in the New Year.
He added: "We are looking to bring players to the club in January, regardless of the injuries.
"Hopefully by that time, Emilio, Cha and Kelvin will be fit but we will have a couple of players maybe coming out of contract near the end of the season and if they are not going to stay then they will have to be replaced."