Costa was involved in a training ground bust-up with Antonio Conte and was subsequently left out of the squad to face the Premier League champions on Saturday (14 January). The former Atletico Madrid forward has been heavily linked with a move to the Chinese Super League with his future at Stamford Bridge in doubt but Courtois believes Chelsea have enough quality to cope with Costa's absence. It remains to be seen if the 28-year-old is included in the squad for Hull City's visit on Sunday.
"Of course we have enough quality to replace Diego," Courtois told FourFourTwo. "Diego is important for us but if he's not there for one game we know we can handle it as well.
"Was this a message to our rivals? Yes, just to see Chelsea won 3-0 and that loss at Spurs didn't affect us and we can play without Diego if need be. I think everybody hoped for us to drop points and we didn't so that was very good."
Conte's men are seven points ahead of second-placed Tottenham, the team who ended their 13-game winning run, and face fellow title contenders Liverpool and Arsenal in the next couple of weeks. Belgium international Courtois knows his side are there to be shot at but thinks their rivals are the ones who are under the most pressure.
"Obviously if you are in front you have the pressure of wanting to keep that gap," Courtois added. "But for us we are there, we are clear at the top and the pressure is more on the other teams than on us."