The US/NATO provide fire control teams, surveillance and intelligence services to Ukraine. They already have many, many "boots on the ground".

Even the Pentagon has officially acknowledged that the US has troops in Ukraine - ostensibly to do inspections and ensure the proper delivery and deployment of the weapons the US taxpayers are sending.

NATO member Poland hardly even tries to pretend that the over 10,000 Polish troops currently fighting in Ukraine are all "volunteers". Indeed, there have already been over 1200 Poles KIA and buried in an "American style" military cemetery.

https://www.republicworld.com/world-news/russia-ukraine-crisis/poles-killed-in-strike-get-american-burial-1200-poles-buried-died-in-ukraine-report-articleshow.html