Blatter, 79 – provisionally suspended from his post for 90 days last month amid the corruption scandal that has engulfed world soccer's governing body – is expected to be released either Monday or sooner, CNN reported.
His adviser and friend Klaus Stoehlker, who spoke with him Wednesday, said Blatter was in a "good mental and physical state" despite his hospitalization in Switzerland, but did not reveal the name of the hospital in question.
Blatter's lawyer Richard Cullen also confirmed to CNN that the Swiss had been in hospital since Friday, but said he had no further comment to make.
Last month Blatter, along with UEFA president Michel Platini, was banned by the FIFA ethics committee.
The sanctions were imposed amid a Swiss investigation into a payment made by Blatter to former France captain Platini in 2011.
Cullen confirmed to CNN via email that Blatter would appeal against the ban, and Stoehlker said he was ready to "fully fight the charges by the FIFA ethics committee."
Stoehlker told CNN: "The ethics committee can't act against an elected official, and the only people who can vote out the president are the 209 associations who elected him in the first place."
Blatter expects to have his appeal heard by the ethics committee either later this week or next week, with the date yet to be confirmed.