Rabada, became IPL's highest wicket-taker with 25 scalps for Delhi Capitals before Cricket South Africa pulled him out as a precautionary measure after he complained of stiff back.
"With KG (Rabada) we are extra cautious because of two reasons," Moosajee was quoted as saying by Cricket South Africa's website.
Mossajee said Rabada will be fully fit within three weeks as his rehabilitation is on track.
"He had a back issue that kept him out of the game for a protracted amount of time. Secondly there's his importance in the squad so we're managing his rehab and his return to play very carefully," the doctor said.
While there was no clarity on when Steyn and Ngidi would get fit, both are expected to travel with the squad to England.
If they don't get fit in time, there are enough players on stand by, said Moosajee
"The selectors have ensured they have enough options on the table but there are some players that have been earmarked as standby players.
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