According to Dave Meltzer from Wrestling Observer, the TLC main event at WWE is scheduled to be Drew McIntyre defending his WWE Championship against Braun Strowman.
The most likely scenario is that Braun Strowman will injure someone on RAW before the Keith Lee vs A.J. Styles vs Matt Riddle number one contenders match for the WWE Championship. Braun will likely attack Riddle before the match so he will be added as a replacement. This is likely just another filler opponent for McIntyre before he moves on to something bigger.