The

The $$Z_{c}(3900)^\pm /Z_c(3885)^\pm $$ and $$Z_{c}(4020)^\pm $$ are two charmonium-like structures discovered in the $$\pi J/\psi $$ and $$D^*\bar{D}^{(*)}+h.c.$$ invariant mass spectra. Their nature is puzzling due to their charge, which forces its minimal quark content to be $$c\bar{c} u\bar{d}$$ ($$c\bar{c} d\bar{u}$$). Thus, it is necessary to explore four-quark systems in order to understand their inner structure. Additionally, their strong coupling to channels such as $$\pi J/\psi $$ and the closeness of their mass to $$D^*\bar{D}^{(*)}$$-thresholds stimulates both a molecular interpretation or a coupled-channels threshold effect. In this work we perform a coupled-channels calculation of the $$I^G(J^{PC})=1^+(1^{+-})$$ sector including $$D^{(*)}\bar{D}^{*}+h.c.$$, $$\pi J/\psi $$ and $$\rho \eta _c$$ channels in the framework of a constituent quark model which satisfactorily describes a wide range of properties of (non-)conventional hadrons containing heavy quarks. The meson–meson interactions are dominated by the non-diagonal $$\pi J/\psi -D^*\bar{D}^{(*)}$$ and $$\rho \eta _c-D^*\bar{D}^{(*)}$$ couplings which indicates that the $$Z_{c}(3900)^\pm /Z_c(3885)^\pm $$ and $$Z_{c}(4020)^\pm $$ are unusual structures. The study of the analytic structure of the S-matrix allows us to conclude that the point-wise behavior of the line shapes in the $$\pi J/\psi $$ and $$D\bar{D}^*$$ invariant mass distributions is due to the presence of two virtual states that produce the $$Z_c$$ peaks