Brown was banned for an additional two matches on top of the automatic one-game suspension for being sent off in the Group H clash against Barcelona on October 1, punishment for flicking a leg out at Neymar after fouling the Brazilian.
The Scotland midfielder, who missed the home game against Ajax last month, was in Switzerland on Friday to plead his case to UEFA's appeals committee, but Lennon said: "It has been turned down. We didn't win the appeal. It is disappointing. We thought we had a good case."
Brown will miss the return game against Ajax in Amsterdam next Wednesday and the visit of AC Milan later in the month.
Lennon, ahead of the Scottish Premiership clash with Dundee United at Parkhead on Saturday, said: "He will be flying back and meeting up with the squad tonight.
"I feel the ban is excessive for a misdemeanour, or whatever you want to call it.
"I am sure we had a fair hearing but it wasn't to be.
"It is a blow for us and for Scott and we will just have to deal with it.
"You are hoping to have the ban reduced but if not, you have contingency plans just in case.
"We do have an idea of who will play there on Wednesday.
"We will have to keep an eye on Beram Kayal, we can't afford to lose too many players in that area because it is a crucial part of the pitch."
- Sports & Recreation