Context. The potentially hazardous asteroid (PHA) (99942) Apophis is one of the most remarkable near-Earth asteroids (NEA) in terms of impact hazard. A good determination of its surface thermal inertia is very important in order to evaluate the Yarkovsky effect on its orbital evolution. Aims: We present thermal infrared observations obtained on January 29, 2013, with CanariCam mid-infrared camera/spectrograph attached to the Gran Telescopio CANARIAS (GTC, Roque de los Muchachos Observatory, La Palma, Spain) using the Si2-8.7, Si6-12.5, and Q1-17.65 filters with the aim of deriving Apophis' diameter (D), geometric albedo (pV), and thermal inertia (Γ). Methods: We performed a detailed thermophysical model analysis of the GTC data combined with previously published thermal data obtained using Herschel Space Observatory PACS instrument at 70, 100, and 160 μm. Results: The thermophysical model fit of the data favors low surface roughness solutions (within a range of roughness slope angles rms between 0.1 and 0.5), and constrains the effective diameter, visible geometric albedo, and thermal inertia of Apophis to be Deff = 380-393 m, pV = 0.24-0.33 (assuming absolute magnitude H = 19.09 ± 0.19) and Γ = 50-500 Jm-2-0.5 K-1, respectively.