Ashwin suffered a side strain while attempting to field off his own bowling during the first one-dayer at the Green Park in Kanpur on Sunday and left the field after bowling 3.4 overs.
He returned to bowl only one more over before hobbling off again, raising doubts about his availability for the rest of the five-match series.
The Board of Control for Cricket in India (BCCI) did not rule out Ashwin, who was playing his 100th one-dayer, but summoned Harbhajan to join the squad as a precaution.
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"After making a detailed assessment of the injury, the medical team will confirm the timeframe required for Ashwin to fully recover from the injury," the BCCI said in a statement.
"Harbhajan Singh has been included in the squad and will join the team before the second match in Indore on Wednesday."
Harbhajan, 35, has claimed 263 wickets in 232 one-day internationals.
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