Hi there,
Right now, SQL Server isn't available for installation on Linux machines. Microsoft announced that want to make it available for Linux on 2017.
But you can install the SQL Server on a Windows Machine and install the Crystal Reports on Linux, because the drivers needed to connect an application to SQL Server are available for Linux. It's called the "Native Client":
Microsoft ODBC Driver for SQL Server on Linux
But the availability of the software doesn't mean that this is a solution supported by SAP, so you need to check the PAM https://apps.support.sap.com/sap/support/pam
Regards,
MM