Dhawan, who had suffered an ankle injury before flying out to South Africa, is set to open alongside Murali Vijay in the series opener at Newlands.
"India opener Shikhar Dhawan is fit and is available for selection for the first Test. Dhawan had suffered a minor ankle injury before the team's departure to South Africa," the BCCI said in a statement.
Jadeja, however, is racing against time to be fully fit for the game and has been taken to the hospital for treatment.
"India all-rounder Ravindra Jadeja has been suffering from viral illness for the past two days. The BCCI Medical Team has been monitoring him and is also in touch with the local medical team in Cape Town," said the BCCI.
"The BCCI Medical Team in consultation with the local medical team has decided that Jadeja will be taken to a hospital for treatment and expects him to fully recover in the next 48 hrs. A decision on his availability for selection for the opening Test against South Africa will be taken on the morning of the match (Friday)," it added.
If India go ahead with the expected three pacers and a spinner combination, Ravichandran Ashwin is likely to get the nod ahead of Jadeja.