-rw-r--r-- 1 clamav clamav 0 Aug 30 2015 /var/log/clamav/clamd.log
and the only permissions needed to stat a file is read permission.
The permissions of clamd.log are ignored when stat(2)ing it. One can stat a `chmod 0' file. What matters is execute permission on the four directories leading to it.
Also, don't trust the error message if it seems incorrect. Track down the cron job and edit it to use strace(1) to learn what system calls fail and how.