The delay is intended to give the team more time to improve "the co-op experience across all game modes, weapon and gadget balancing, as well as menu and interface navigation," according to a blog post from Ubisoft.
The Rainbow Six Siege beta will still launch on time Sept. 24, Ubisoft added, with the delay providing the team with more time to test network elements like infrastructure and matchmaking.
The decision to delay the game was spurred in part by both internal playtesting and gameplay sessions at both E3 and Gamescom, according to Ubisoft.
In recent years, Ubisoft seems more willing to delay games that it feels don't meet its internal expectations. This trend seemed to kick off in 2013, when the company announced last-minute plans to delay Watch Dogs. At the time the developer and publisher also delayed The Crew. The company also delayed South Park: The Stick of Truth in 2013 and Assassin's Creed Unity last year.
Earlier this year, Ubisoft announced it was pushing back the release of The Division to 2016.
Rainbow Six Siege is coming to PlayStation 4, Windows PC and Xbox One.