Mr Wigley, 56, will convalesce at home in the village of Bontnewydd in his Caernarfon constituency. Ieuan Wyn Jones, the MP and Assembly member for Ynys Mon is expected to be temporary group leader in the Assembly. Mr Wigley remains party president.
Earlier this year Mr Wigley confirmed he would not contest the next general election so he could concentrate on the Assembly. Plaid has already selected Hywel Williams, a social policy lecturer, as its candidate to defend Mr Wigley's 7,449 Westminster majority.
Mr Wigley was elected to Parliament in February 1974, and is credited with masterminding Plaid's success in last May's Welsh Assembly elections. The party won 17 of the 60 seats to become the main opposition to Labour.