Krishna raised Sarabjit's case with Zardari during a meeting last night.
"The President has taken it very seriously and he instructed his office to look into the details," Krishna told Indian reporters during an interaction here this evening.
"Our approach is on a humanitarian basis, especially the fact that he has spent almost 20 years in a Pakistani jail," he said.
The Pakistan government will have to consider factors like Sarabjit's age and health while deciding on the issue, Krishna said.
Sarabjit was convicted for alleged involvement in a string of bombings in 1990 that killed 14 people.
His family says he is a farmer and the victim of mistaken identity.
Sarabjit's relatives said he strayed into Pakistan in an inebriated state three months after the bombings.
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Following the intervention of the Pakistan People's Party-led government, Sarabjit's execution was put off indefinitely.
He is currently being held at Kot Lakhpat Jail in Lahore and recently submitted a fresh mercy petition to President Zardari.