Manager Maurizio Sarri was left furious on the sidelines when the Spaniard refused to be taken off minutes before a penalty shootout against Manchester City.
Kepa remained on the pitch and saved Leroy Sane’s spot-kick but Chelsea eventually lost 4-3.
Sarri insisted after the match that the whole episode was down to a misunderstanding about the goalkeeper’s condition, but Ballack thinks that Blues players should have done more to make Kepa follow his manager’s instructions at the time.
“It was surprise, I’ve never seen anything like that before,” the German told talkSPORT.
“When your number is shown, you must respect the manager’s decision.
“I was a bit surprised by the reaction of the team. Normally if a team-mate is not leaving the pitch and is frustrated for a certain reason, and obviously this was a really important reason to make a quick sub just before the penalties, you go over and you try to speak with him to get him to follow the instructions.
“But David (Luiz), I don’t what he was saying to him, but he’s a key player in that team and he’s a leader, so it surprises me.
“It was a not a good picture for Chelsea.
“The board has to say something because it’s really, really important the players respect the coach and respect each other and something shouldn’t happen like that.
“It was a shame, because they played a good game against a really strong team and they deserved something, but now we’re all talking about something like this.”
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