Chelsea striker Diego Costa could miss the season opener against West Ham United after suffering a back problem.
The Spaniard didn't train with the rest of the squad before the game against Real Madrid and could be ruled out for weeks.
The Italian admitted that he was disappointed with the news as it prevented him from utilising the 27-year-old during his latest training sessions.
"I have to see the players in training. If I cannot see them in the training session, I cannot put them in a game," Conte told reporters.
"I want to see my players in training, doing the work.
"If someone is injured or there is some problems and I don't see the player, then it's impossible for me to think about putting him in the starting eleven or on the bench.
"This is normal, for me. In the last few days, Diego had pain in his back. So he didn't train, and for this reason he didn't play."