Karthik is expected to join the team ahead of the final Test at the New Wanderers Stadium in Johannesburg.
"The All-India Senior Selection Committee has named Dinesh Karthik as replacement for Wriddhiman Saha for the third and final Test against South Africa," the Board of Control for Cricket in India said in a statement.
"He is set to join the team before the third Test."
Saha, who suffered a hamstring injury while training ahead of the ongoing second Test at Centurion, will be under the supervision of the board's medical team.
"Saha suffered an upper left hamstring tendon injury during training on Thursday. The BCCI Medical Team will continue to monitor his progress," the statement added.
Veteran stumper Parthiv Patel is currently donning the big gloves in the second Test.
India currently trail the Proteas 0-1 in the three-match rubber, having lost the opener in Cape Town.
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