Wales bring in Williams for Webb
Wales bring in Williams for WebbSHARE
Allen (four caps) links up with the squad after Newport Gwent Dragons centre Tyler Morgan was released due to a hamstring injury.
Uncapped scrumhalf Williams is called in as injury cover following Rhys Webb's injury against Australia on Saturday.
It is feared that Webb suffered serious damage to his ankle ligaments and could miss the rest of the November international window.
Medical update on injuries will be made following further assessment.
Additional source: express.co.uk