Rovers have handed Bain a contract until next summer after the Grenada international striker impressed Barnes while on international duty.
Bain goes straight into the squad to face the Saddlers as Barnes seeks to avoid a fifth successive defeat in League One.
On-loan Blackburn defender Gavin Gunning returned to Ewood Park after the 3-0 defeat at Carlisle last Saturday.
Marlon Broomes looks set to challenge club captain Ian Goodison and young prospect Ash Taylor for a centre-back berth but right-back Shaleum Logan is suspended.
The on-loan Manchester City defender was sent off at Brunton Park and serves a one-match ban, while striker Bas Savage (Achilles) remains a long-term absentee.