We investigate the fluctuations of linear spectral statistics of a Wigner matrix W N deformed by a deterministic diagonal perturbation D N , around a deterministic equivalent which can be expressed in terms of the free convolution between a semicircular distribution and the empirical spectral measure of D N . We obtain Gaussian fluctuations for test functions in C 7 c pRq (C 2 c pRq for fluctuations around the mean). Furthermore, we provide as a tool a general method inspired from Shcherbina and Johansson to extend the convergence of the bias if there is a bound on the bias of the trace of the resolvent of a random matrix. Finally, we state and prove an asymptotic infinitesimal freeness result for independent GUE matrices together with a family of deterministic matrices, generalizing the main result from [Shl18].