West Ham's Jack Collison has been drafted in to replace Brighton and Hove Albion midfielder Crofts, who is suffering from an ongoing groin problem.
West Brom goalkeeper Myhill misses out with an Achilles tendon problem, and Vaughan, on loan at Nottingham Forest from Sunderland, is sidelined with a hamstring injury sustained in training.
Chris Coleman is no stranger to player withdrawals, the Wales boss having been forced into calling up nine replacements for the last two 2014 FIFA World Cup qualifiers against Macedonia and Belgium in October.
This weekend's clash takes place as doubt remains about Coleman's future, though reports in recent days suggest progress is being made in contract talks.
Finland will be looking to bounce back from a 3-0 defeat to France when they meet Coleman's men in Cardiff.
