Lambert may have performed a minor miracle in his 20 months at the helm, but the former Champions League winner knows the biggest test of all lies ahead when the squad regroup for pre-season training.
"I think they know the magnitude of it, they know what I expect and I have no worries about any of them," said the 41-year-old.
"I have no worries they won't come back in good shape. This is too big for us not to be ready.
"It is the best league in the world that you are going to play in, you are up against the best players and if you come back and you are not ready for that then there is only one person to blame.
"It ain't going to get any bigger than this - we are right in it now, that is the bottom line, there is no room for error."