The Packers are serious about challenging Anders Carlson. Per Bill Huber at SI.com, they worked hard to get an unidentified veteran FA, and both sides had agreed to a deal. Before actually signing, the kicker changed his mind and signed with a different team.

The only veteran FA kickers who have been signed are:

Wil Lutz
Nick Folk
Brandon McManus
Joey Slye

Seemingly, it would have to have been one of those four.