Cape Town - Chelsea manager Guus Hiddink admits he spoke privately to Baba Rahman following the youngster's mistake against Southampton over the weekend.
A poor header from the Ghanaian in the 42nd minute allowed Shane Long to race through and open the scoring for the Saints.
Hiddink didn't waste any time to replace the left-back as he brought Kenedy on after the half-time break and Chelsea went on to win the game 2-1 thanks to second-half goals from Cesc Fabregas and Branislav Ivanovic.
"He has to recover," Hiddink said of Rahman.
"You cannot always wait [to make substitutions] and we need everyone. He did some decent play in the recent games but we also like to be critical and defensively you have to do your job as well.
"I talked to him and Steve [Holland] talked to him as well. You saw when he put his shirt over his face on the pitch, he was thinking 'Oh what did I do now'.
"At half-time he was sitting in the dressing room [feeling] down before I announced it. Not just [because of his reaction] but that's why we made the change."