From this interview in England last September, author Lee Child mentions Fredrick Forsyth.
I think that Without Fail  would actually be my homage to Day of the Jackal, because it explicitly references Forsyth’s book. The emphasis there is placed upon the assassins planning for escape, as opposed to the  Clint Eastwood/Wolfgang Peterson film, In the Line of Fire, in which the assassin knows he won’t be able to escape. As I said at the CWA Diamond Daggers ceremony, The Day of the Jackal … was Year Zero for the current generation of thriller writers; it was different, and re-set the clock, and we’ve all had to deal with it ever since. So, I didn’t mean it as a direct homage but acknowledged–for all of us, readers and writers–that Fredrick Forsyth is a giant figure, and his debut novel casts a giant shadow over the genre.