Commentaire sur Le Lévitique 27:11

ואם כל בהמה טמאה AND IF IT BE ANY בהמה טמאה — Scripture is really speaking here not of an “unclean" but of a blemished animal which ,is just on this account, unclean (i. e. unfit) for sacrificing, and Scripture is telling you that sacred animals which have no blemish cannot again become non-holy (more lit., go forth from the category of holy animals to that of non-holy animals) through redemption except if they become blemished (Temurah 32b; Sifra, Bechukotai, Section 4 1).

ואם כל בהמה, an animal already sanctified as a sacrifice which had in the meantime become ritually unclean so that it no longer qualified for the altar because it had developed a physical blemish;

A blemished [animal]. Rashi’s proof of this is from the end of the section (verse 27) where it is written, “If it is of an unclean animal...” There one is has to say that it is speaking of an actual unclean animal, and it is connected to this verse [which speaks of exchanging animals for animals], as Rashi explains there. If so, this indicates that [here] it is speaking of a blemished animal (Re’m). Alternatively, Rashi derives this since it is written, “Which cannot be offered to Hashem.” This is superfluous as it is obvious that one cannot offer unclean animals to Hashem. Thus it teaches that the verse is speaking of a blemished animal.