Niemi was claimed on Tuesday, a day after being waived by the Pittsburgh Penguins. He allowed 16 goals in losing three games for the Penguins. Niemi is now on his third team in four months and fourth since winning the 2010 Stanley Cup with Chicago.
He signed with Pittsburgh in free agency last summer after being released by Dallas in June.
Luongo has missed one game since being hurt in a 4-3 loss to Pittsburgh on Friday. Harri Sateri, who has yet to appear in an NHL game, was called up to back up James Reimer.
The Panthers are at Montreal on Tuesday to close out a two-game road trip.
The New York Rangers placed forward Adam Cracknell on waivers.