In October, the International Trade Commission ruled in Masimo's favor, prohibiting Apple Watch Series 9 and Ultra 2 imports.
Apple temporarily removed the affected watches from its online and retail stores in December, although existing stock at other retailers remains available.
Recent court filings indicated that Apple obtained US Customs approval for a modified version of its Apple Watches without the blood oxygen feature.
It potentially paves the way for the modified watches to return to US shelves.
Apple has yet to comment on the Customs decision.
Masimo's allegations extend beyond intellectual property, accusing Apple of recruiting top executives and copying technology after a declined partnership.
The latest ban could pose challenges for Apple's in-store repairs, as the affected watches may be unavailable in US stores.
Apple has not issued a comment on the recent denial.
