Marin Cilic's ban for doping has been reduced from nine months to four, allowing him to play at the Paris Masters next week.
The Court of Arbitration for Sport says the International Tennis Federation ban was "too severe in view of the degree of fault."
The 25-year-old Croatian will be cleared from midnight Friday.
Cilic tested positive for a banned stimulant, nikethamide, at a tournament in Munich in May. Cilic claimed he did not intend to ingest the substance in glucose tablets and challenged his ban at CAS.
The ITF requested a two-year ban from CAS by appealing the verdict of its own independent tribunal.
Cilic's ranking peaked at No. 9 in February 2010, and has dropped from 12th to No. 47 since accepting a provisional suspension in June.