Lonergan, who would have played on Lance Franklin, hasn't recovered from the bout of concussion he suffered in last Friday's win over North Melbourne.
"Tommy won't get up," Cats football manager Neil Balme said.
"Unfortunately, there hasn't been enough time to go through the process with him.
"There's an argument that he could be OK by game-time, but we just don't take that sort of risk."
Enright, who turns 33 in September, suffered an ankle injury in the victory over the Kangaroos.
Balme said the injury was a cartilage problem and was expected to sideline Enright for only one week, although he added that the time-frame was uncertain at this stage.
"He's a bit sore," Balme said.
The Cats will welcome back midfielder Steve Johnson from suspension for Thursday night's big clash with the Swans.
They are also set to have one surprise inclusion, with Billie Smedts and yet-to-debut draftees Darcy Lang and Brad Hartman among the travelling party.
Smedts only played his first game of the season last weekend in the VFL.
He had previously been sidelined more than two months by the fractured leg he suffered in the club's final practice match.
"We've been pretty conservative (with his recovery)," Balme said. "He's done a lot of running, so he's very fit and he looked pretty good last week in the VFL.
"With blokes who've got talent, why waste them? And it's kind of exacerbated a bit by the VFL's got a bye, so it's not as though he could play another full game."
Smedts is expected to be named in Geelong's team on Wednesday night, although either of Hartman or Lang could be a late inclusion prior to the game.
"There's a few doubts around the place because of the two lots of (six-day breaks) and the two lots of travelling over three weeks," Balme said.
