Based on the latest info from the wiki (updated Sept 17), Zay Flowers' Week 2 status is uncertain — he's day-to-day with a hamstring injury after putting up monster numbers (5 rec, 150 yards, 1 TD) and then exiting early in Week 1. The injury isn't considered serious, and he left out of "an abundance of caution," but he missed Wednesday practice and his availability against the Saints is pending further tests (from the Zay Flowers page).
Sal Vetri offered a harsher take on hamstring timelines for WRs:
"For hamstrings, it's three to five weeks for a wide receiver depending on severity. Week 2, him playing week two would be a major outlier." —
So the official line is day-to-day and not serious, but hamstrings are notoriously tricky. I'd keep an eye on Friday's practice report — if he's limited or out again, that's a bad sign for Sunday. If he doesn't go, guys like Rashod Bateman and the rookie Ja'Kobi Lane would see more targets in a great matchup against a weak Saints team.