The social network is currently testing the feature, and it would mean users will turn to a single app to access both the platform itself and elements of its messaging service.
As noted by app researcher Jane Manchun Wong, the change would still use the Messenger button currently seen in the Facebook app, but this would instead open a new 'Chats' section instead of opening the separate app.
It has been half a decade since Facebook opted to remove the Messenger functionality - which was first released as a standalone service in 2011 - from its main app.
It comes as the company is looking to integrate its messaging services across Instagram, Messenger and WhatsApp.
Wong added that it's likely both the new feature and the standalone app will remain though, as they "serve different markets".
She added that the new section of the app is a basic version of the Messenger app, and as such as it doesn't include features like calling, sending photos and more.
She tweeted: "For now, this new 'Chats' section seems to only contain the basic chat functionalities. To give message reactions, make a call, send photos, etc, you'd still have to open the Messenger app."