The ground state of the frustrated A-site magnetic spinel CoAl 2 O 4 has been a controversial issue whether it is a collinear antiferromagnetic ordering or a spiral spin -liquid state, as the ratio of the two competing interactions, J 2 /J 1 lies close to the boundary between these two ground states.Here, we address the magnetic ground state in CoAl 2 O 4 with different amount of Co 2+ /Al 3+ site disorder from the study of magnetoelectric effect and Monte Carlo simulations. CoAl 2 O 4 with low site disorder exhibits linear magnetoelectric effect below the magnetic ordering temperature.With increasing disorder, the magnetoelectric effect is suppressed and the sample with 14% disorder exhibits a spin glass behavior without the magnetoelectric effect. Monte Carlo simulations support the experimental findings and suggest that the site disorder suppresses longrange antiferromagnetic order and induces a spin glass state. Since the linear magnetoelectric effect requires a long -range magnetic ordering, we suggest that the ground state of CoAl 2 O 4 with low site disorder is a collinear antiferromagnet. PACS number(s): 75.47.Lx, 75.50.Ee, 75.85.+t *E-mail: sundaresan@jncasr.ac.in spin -liquid states [1,2]. Many contradicting experimental results have been reported regarding the true nature of the magnetic ground state of CoAl 2 O 4 . In an earlier report by W. L. Roth, using neutron diffraction experiments on a polycrystalline sample of Co 1-x Al x [Al 2-x Co x ]O 4 with an antisite disorder of x = 0.05, which hereafter will be represented as CAO:0.05, a collinear antiferromagnetic ordering of Co 2+ spins at 4.2 K was suggested from the observation of a weak magnetic Bragg peak at (200) position in neutron diffraction pattern, similar to the arrangement of Co 2+ spins in Co 3 O 4 [5]. Later, a spin glass state was proposed using magnetic, electron spin resonance and heat capacity measurements in CAO:0.08 [8]. Recently, Kenataro Hanashima et al. investigated a series of compounds with different degree of disorder (x) and have shown that the spin glass state is present with higher degree of disorder (x 0.10), while the magnetic state changes to spiral spin -liquid state as it becomes more ordered (x 0.06) [9]. Based on inelastic neutron diffraction experiments on CAO:0.07-0.08, Krimmel et al. have shown that J 2 /J 1 ~ 0.17 > 1/8 and concluded the presence of spiral spin -liquid state with a very strong but short -range spin correlations [3]. The presence of spin -liquid like state is also supported by the results of the neutron diffraction experiments on single crystal of CAO:0.08 by Zaharko et al.[2]. Later, they reported that the magnetic ordering is unconventional and its bulk magnetic properties are isotropic [10]. On the other hand, it has been shown that these properties are anisotropic microscopically as inferred from neutron diffraction experiments under magnetic fields [10]. On the same sample, using local spin probe techniques such as electron spin resonance, nuclear magnetic resonance and muon spin relaxat...