Muamba was released from hospital on Monday, a month after he suffered a cardiac arrest at Tottenham that stopped his heart for more than an hour.
Coyle said: "I'd come in from training and Shauna sent me a message: 'There's somebody who'd like to speak to you.' And when I spoke to him, you can always tell from the sound of somebody's voice and he sounded in a good place.
"It was great to hear from him and he sounded terrific. Of course, that's a huge boost given where he's come from. We've all seen the sad events in Italy."