Carayol underwent knee surgery in April after damaging knee ligaments against Bournemouth.
There was some hope that the Gambian winger may be ready for August, but Boro are not rushing him and head coach Aitor Karanka admits he will not be involved.
"Unfortunately, we don't expect Muzzy to be ready for when we return to training," confirmed Karanka. "He will miss a chunk of that training.
"It has been tough for Muzzy to have such a serious injury, but I am in contact with him every week and he is stronger each time I speak to him.
"His mentality is stronger each day. He will have a bit of a break now because he has been working very hard and he needs a change of scene, but after that, he will return here to rehab."
Williams suffered an Achilles injury in January, which has subsequently ruined his World Cup hopes, with the finals coming just too soon for the 25-year-old.
But the Boro academy product will be ready to return to the first-team squad ahead of pre-season.
"Rhys should be fit for the start of pre-season," said Karanka. "His recovery is coming along very well and we are happy with where he is in terms of his fitness. He should be able to join up with everyone when we all come back to start the preparations for next season."
Meanwhile, another player who will be involved in pre-season will be David Atkinson - who has agreed a new one-year deal The Riverside.
The 21-year-old has been heavily involved in the first-team in recent weeks and has regularly made the bench - although he is yet to make his debut.