The Scot has spoken of the complications in keeping his squad happy, after rotating his starting line-up for Saturday's goalless draw with Stoke City in the Premier League.
Nicolas Anelka was named among the substitutes, while five senior players - Goran Popov, Steven Reid, Graham Dorrans, Markus Rosenberg and Diego Lugano - failed to make the matchday squad.
"The hardest part for me is picking the team," he told the Birmingham Mail.
"But now also picking the bench and choosing who to leave behind is also difficult.
"I was without five senior players who didn’t even travel.
"I need to manage the players and make sure I get the best from them.
"Even if they are not involved, that’s my job as head coach - I need to do that to the best of my ability so when they are selected they are ready to go."
He continued: "I've got a good squad of players who, at different times, different people will start games.
"You look at the bench and the players I didn't even bring. So we’re really strong in that respect.
"At times players will have to miss a week, maybe a couple of weeks. Nicolas' (Anelka) answer, for instance, was to come on and do well.
"We made some changes and the boys who came into the game certainly contributed to us finishing well."
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