Platini, the suspended head of European football confederation Uefa, will challenge his six-year ban at the Court of Arbitration for Sport (CAS) in Lausanne, Switzerland on Friday.
“Blatter will testify on Friday, at the request of Fifa”, said a source who was not authorized to discuss the case publicly, but confirmed the information first reported by L'Equipe newspaper.
In December, Fifa's ethics judges found Platini guilty of ethics violations, conflict of interest and other offences in connection with a two million Swiss franc ($2 million, 1.8 million euro) payment he received from Blatter in 2011.
Both men claim the payment was part of a legitimate oral contract for consulting work that Platini did between 1999 and 2002, but Fifa's in-house court found that explanation unconvincing.
The pair were first suspended for eight years in December, but a Fifa appeals panel reduced the bans to six years in February, citing mitigating circumstances.
Uefa has said it will not replace Platini until all his appeals are exhausted, while CAS has indicated it would rule on the Frenchman's case before the June 10th start of the Euro 2016 tournament, which is being hosted by France.
If Platini's appeal is successful, he could reclaim his Uefa post in time to preside over the tournament.