According to recent news from Poland, Polish troops are already in Ukraine, but they are not officially under the Polish flag. Here is an excerpt of the English translation:
In Kiev, the beginning of the formation of the first Polish special unit subordinate to the Ministry of Defense of Ukraine was announced. Poles will perform reconnaissance and diversionary tasks. The elite unit will receive the most experienced soldiers, including volunteers fighting against Russia . . . Probably our unit will be called Polish Volunteer Legion. Its organization is carried out by an unnamed citizen of Polish, who has been fighting Russia in Ukraine since the beginning of the Russian invasion. The organized unit will not be a typical front unit, like those in the international legion, but will deal with reconnaissance and diversion. W Ukrainie powstaje pierwsza polska jednostka specjalna - WiadomoĹci
The status of the Polish troops may change if the Ukrainian army starts to collapse.
Politico is saying that Ukraine already has over 100,000 killed in action. That is more than the total US losses for all the wars since WW2, and the US is over ten times the size in terms of population.
The collapse of the Ukrainian Army is a question of when rather than if. The only exception would be is a sudden end to the fighting, but instead the US has been promoting fantasies about a successful Ukrainian offensive.