Conte said, "For a striker, to spend 55m Euros [£58m] on a young player like Morata, and selling Costa for 60m [£60m] Euros, a player older than Morata... that was a good sign for the club."
It is believed that Morata picked up his back issue last Friday, a day before Chelsea took on Brighton at the Amex Stadium.
Conte admits he doesn't know how serious the injury is, but hopes Morata will be fully fit again soon because of his lack of striking options in his squad.
"If you remember, in the past, he stopped himself for a problem in his back. A pain in the back. Now this pain has come back," Conte said.
"I hope it's not serious. But this is the second game that he stopped. He wasn't available against Brighton because this problem was there the day before as well [regardless of his suspension]."