You're using a query select field so no that won't be possible since it has no means of passing the selected value through substitutions as nested substitutions are not allowed in normal circumstances. It should be doable with a code field provided by CB Code Field using PHP and getFields API. Example as follows.
Code:
return \CBuser::getInstance( (int) '[FIELD_NAME]', false )->getField( 'avatar', null, 'html', 'none', 'list', 0, true );
Replace FIELD_NAME with the name of your field, which should be a user id. It'd be possible with normal substitutions if the user attribute in substitutions supported a field (e.g. user="FIELD_NAME"), but at this time it does not so have added a feature ticket for that.
forge.joomlapolis.com/issues/7824