Platini saw the FIFA presidency as his destiny, but the UEFA leader was prevented from running in February's election when a payment of 2 million Swiss francs (USD 2 million) from the global governing body was exposed.
Instead, Infantino was plucked from the relative of obscurity of the UEFA general secretary job to become Europe's candidate to succeed Sepp Blatter.
Infantino received the news that the Court of Arbitration for Sport had reduced Platini's ban to four years while in Mexico City preparing for his first congress as FIFA president.
"Obviously as FIFA president I need to respect the decision of the CAS, there is no doubt about that," Infantino said. "On a personal level, of course, I am very sad about the decision. I have worked with Michel for the last nine years in UEFA, seven as general secretary. All together we did some great things. And I really want to keep these positive memories, at this moment focus on the positive memories."
The CAS panel ruling clears a potential barrier to Infantino seeking a second term leading FIFA. The election will be in approximately May 2019, and Platini will remain banned until late 2019.
FIFA's ethics committee provisionally suspended Platini along with Blatter in October and then banned them for eight years in December.
FIFA's appeal panel cut two years off their sanctions in February as reward for their long service to the sport.
Both men are appealing to CAS, but Platini's case was heard first, and another two years were slashed from his ban.
CAS said it was "not convinced by the legitimacy" of Platini being paid 2 million Swiss francs by FIFA in 2011, nine years after his work as a Blatter adviser ended when he joined the executive committee.
Asked if FIFA would now seek to reclaim the cash, Infantino said: "Now is not a moment to speculate about these things."
Infantino hosted the first meeting of the FIFA Council, which has replaced the discredited executive committee following far-reaching corruption and bribery scandals.