Warhammer 40K: Space Marine has failed to appear on the UK Steam store, despite the PC version using Steamworks.
Space Marine's demo similarly failed to turn up last month - with no explanation given.
Another THQ title, Saints Row: The Third, is also missing from the service.
UK retailer Game has strongly denied rumours it is to blame, after a whistleblowing report accused the shop of asking publishers to remove games from Steam in a bid to stifle its digital competitor.
Brink initially failed to appear on the UK Steam store without explanation, although did eventually release. It was suggested publisher Bethesda was asked to keep Brink off of Steam until a month after its retail launch.
Digital versions of Space Marine's PC edition are still available at Direct2Drive and Gamersgate for £35, or via ShopTo.net for £23 (thanks, RPS.
Space Marine developer THQ has refused Eurogamer's repeated requests for comment.