The announcement of the new candidate will be made shortly, said AAP state convener Gurpreet Singh Ghuggi.
Lal was admitted to a hospital since last three days and was unable to campaign in the area, he said.
Lal is a former Congress leader.
AAP has announced candidates for 110 seats while its ally Lok Insaaf Party (LIP) is contesting on seven seats.
Punjab has 117 assembly seats.