Allen, (4 Wales caps) links up with the squad after Newport Gwent Dragons centre Tyler Morgan was released due to a hamstring injury.
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Uncapped scrum-half Williams is called in as injury cover following Rhys Webb’s injury against Australia on Saturday.
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Medical update on injuries will be made following further assessment.
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Wales squad update
Wales have called Cardiff Blues duo Cory Allen and Tomos Williams into their 2016 Under Armour Series squad.
