How is it possible for a Yisrael to have no relatives?
Rashi and Targum Yonasan: The Pasuk means relatives who have the means to redeem the field.
Moshav Zekenim: It can mean that his relatives do not want to redeem it, One opinion (in Kidushin 21a) learns from here that they are not commanded to redeem it. 1 (The other opinion obligates.)
Moshav Zekenim: Why is this unlike "Ein la'Ish Go'el" (Bamidbar 5:8)? Bava Kama 109a learns from there that it discusses a convert, who has no relatives! (Perhaps this opinion holds that it is unreasonable to obligate relatives to redeem. That verse discusses returning theft to a relative if the Nigzal died. We cannot say that no relative wants to take it!
What does the word "u'Matza" mean?
Rashi (in Bamidbar 11:22): It means that he obtains the means.
Erchin, 30b: It precludes selling a distant field in order to redeem one that is close or selling a poor-quality field in order to redeem a better-quality one. 1
Since "u'Matza" implies that he obtains the means now and not that he already had it.