It's uncertain right now, but the odds are not in his favor.
Lamar Jackson sprained his ankle on the final play of the first half in Week 4 against the Titans, left the stadium in a walking boot, and didn't return (from the Lamar Jackson page). Per Ian Rapoport, he has an "outside chance" of playing Week 5 vs. Atlanta, with Monday's MRI results set to provide clarity. Backup Tyler Huntley filled in well (8/9 passing) in the Week 4 win.
On Flock Fantasy, the take was more pessimistic: "There is a high probability that Lamar Jackson will miss Week 5" — with the markets already pricing that in [].
Bottom line: He's more likely out than in for Week 5. Monitor the Monday MRI news for the final word.