The Blues only retained their second-tier status with a draw at Bolton Wanderers on the final day of the campaign, and Clark has revealed that his players, many of whom have been signed this summer, are pushing each other for starting roles next month.
The 41-year-old is quoted by the Birmingham Mail as saying: "They've been fantastic. All of them are pushing each other.
"With each week that goes by, there is a different test and the pressure starts to mount on them because they're running out of games and training sessions to be on that team sheet for Middlesbrough and our first Championship fixture."
Birmingham continue their pre-season with a friendly at Mansfield Town on Saturday afternoon.