Lancaster had several international hits with the group during the 60s and 70s including Rockin' All Over The World and Whatever You Want.
Manager Simon Porter said: "This is such sad news."
Lead singer Francis Rossi said: "Alan was an integral part of the sound and the enormous success of Status Quo during the 60s and 70s."
Rossi and Lancaster began performing together in the 1960s under a number of different band names before settling on Status Quo.
The group went on to have four UK number one albums, according to the Official Charts Company.