Blues boss Paul Lambert says Alan Judge and Anthony Georgiou have both done well when they have played this season but that no one can expect to play week in, week out.
Judge, 30, was left out of the side which won 1-0 at Fleetwood in the Blues’ last League One outing having started the previous two games.
Georgiou, on loan with the Blues from Spurs until January, is still to start a first-team game having made five substitute appearances in League One.
"As a footballer, nobody in their right mind can expect to play unless you're Messi or Ronaldo.
"If you go down that road then I think it's a dangerous game, you've always got to look over your shoulder.
"Judgey's done well when I've asked him to play. I changed the team for Fleetwood because I thought it was going to be one of those types of games.
"There will be games when I'll say Judgey's in, and that's the case with everybody. I don't think as a footballer you start to think you're a shoo-in unless you're Messi and Ronaldo, I don't think anybody else can do it.”
Georgiou has missed out on a chance to start in the Leasing.com Trophy action as he has been away with Cyprus during both international weeks.
"He's been called up for his national team, and you can't curtail that,” Lambert said.
"Anthony changed the game in our favour against Wimbledon. It was a massive result because we were 1-0 down and he came on at half-time and I thought turned the game on its head.
"He's unfortunate because the lads have been playing so well, but every time I put him on, he's performed.
"You can't stop anybody going for their national team, if he was here for it he'd have played in the cup, but the national team is important to him.”
He added: "He's done great, as I've said before, I'm really happy with him. He'll probably want to play more games, but I think he understands it.
"But every time I've asked him to perform, he's stepped up to the plate and made us look lively again.”