connecting 2ch amp and AVR into same sub

Hi there. I was wondering if someone could help me with some connection concerns. I currently have my 2ch amp connected into a sub for music but have just purchased an AVR for movies which I also want to connect into the same sub. The amp has L and R sw cables going into the sub’s phono inputs. Can I connect another sw cable from the AVR into the sub’s left phono input via a 2into 1 adapter? Or, will this be disastrous? Only one of either the 2ch amp or AVR will be used at the same time. Thanks for your help.