Yaakov told/commanded Yosef (not prophecized) that Yosef's two sons, Efrayim and Menashe, would become tribes on par with those of Yaakov's own sons (B'reshis 48:5):
וְעַתָּה שְׁנֵי־בָנֶיךָ הַנּוֹלָדִים לְךָ בְּאֶרֶץ מִצְרַיִם עַד־בֹּאִי אֵלֶיךָ מִצְרַיְמָה לִי־הֵם אֶפְרַיִם וּמְנַשֶּׁה כִּרְאוּבֵן וְשִׁמְעוֹן יִהְיוּ־לִי׃
Now, your two sons, who were born to you in the land of Egypt before I came to you in Egypt, shall be mine; Ephraim and Manasseh shall be mine no less than Reuben and Simeon.
However, he didn't bless them among the tribes.
Why?