He was substituted in Wednesday's defeat by Canada and was seen to be upset.
"People say he was crying but I know he had a few problems with illness in the week and he came off in the game and I know he cares deeply about playing for his country," points out Lampard, "so I don't think we should jump to conclusions on that.
"Emotion is not the worst thing to see, whichever way it comes out, and I am completely with him. He needs, as every player in the squad does, to work hard in training, keep improving daily in training and see the direction we are going in and be a part it.
"Players need to show what they can give on a match day, it is the same for all the players, and Christian is no different from anybody else."