The pair were signed as Michael Bradley made the move to Toronto FC.
Garcia said: "We are stronger now with these two players, as they give us more solutions. [Michael] Bradley may have left, but Nainggolan's arrival means that we have maintained numerical parity in midfield.
"Bastos provides us with more options going forward, especially on the flanks. With [Federico] Balzaretti injured, he also presents us with a defensive option. He still has to do work to get to the physical level expected, but he will start training."
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