Powerful centre-half Moore played a key role in West Brom's two promotions under Megson and looks surplus to requirements at the Hawthorns, especially if manager Bryan Robson is successful in a move for Middlesbrough's Ugo Ehiogu.
31-year-old Welsh international Johnson left Forest for the Baggies in 2001 after making over 100 appearances for the Reds.
Like Moore he appears to have little chance of first-team action at the Hawthorns, having made just four appearances so far this season.