Too bad about Ljubo, but at least he's being replaced by another Croat
At the US Open Roko is only defending 8 points (he won one match in qualies last year) so even if he loses in the first round (worth 5 points) this year, he'll only lose 3 points. On the other hand, if he wins his first match he'll likely move into the top 90, for a new career-high ranking.
Good luck, Roko. Hope you get a winnable first-round match. (I hope I'm not jinxing him!)