User blog comment:FairyRaven/Fairy Tail Chapter 471: Until the Battle is Done, Review and Commentary/@comment-70.179.149.246-20160202003956/@comment-7418318-20160202093030

Or maybe he didn't look worried over Serena because he doesn't care about him.

That he cares about the other Spriggans (if he really does care about them as people, rather than just battlefield ressources) doesn't necessarily include Serena. He might see him as a betrayer to his home country and thus a person not to be trusted.

Maybe August allowed Serena to fight the Wizard Saints on his own exactly because he didn't trust him or maybe even secretly hoped that Serena would perish or as a test to find out if he's truly loyal to Alvarez.

So many possibilities.