Walker appealed to referee Matteo Marchetti against a red card shown to Alli, who was making his debut for Como at the San Siro after a long time watching on from the sidelines in a difficult part of his career. The 28-year-old is a former teammate of Walker and they spent many years together at Tottenham before Ali fell out of favour.
Speaking on the Kyle Walker podcast, the City star revealed that facing 10 men on the day was a welcomed opportunity but seeing his friend be sent off after returning to football was hard to take.
"I think my heart kicked in. Anyone else, I would have just let him get sent off. Especially a man down at the San Siro, you think, okay, we go and do what we've got to do.
"I know what he's tried to do. We've all done it where you just clip the ankles of someone and they don't get the counterattack. But maybe where he's not played for a couple of years and is out of the rhythm of the game and everything like that, he's caught Ruben (Loftus-Cheek) a little bit too high. And that was it.
"Of course, I think in footballing terms, we need ten men. We want the ten men, AC Milan want the ten men. But for the personal relationship that I have with Dele, for the number of years that I've known Dele, for what he's been through — which obviously he's publicly said and I think he's been very strong and open about that and very brave in coming out and saying what he said — to finally come back after such a long time of being out, to then get sent off for a not really cynical challenge. I think your heart just kicks in, as I said at the start.
"I went to see him after because he's a great friend of mine. And he was down, he was disappointed.”
Ali has the chance to turn his career around in the Serie A under Como manager Cesc Fabregas and Walker believes he could return to his old self as he works hard behind the scenes to recover his form.
"He was frustrated with himself for the decision. But there were no hard feelings from Ruben (Loftus-Cheek). I think they actually got a plane on the way back home (to England) together. That was the rumour.
"Dele came to the dressing room after (to see Ruben). He was hugging. It's just football. We move on from it. And you know, Dele has to move on from it, very quickly, to make sure that he's back to where he needs to be.
"I know how hard he (Dele) has worked, especially off the field. And then to get his chance now at Como, I think it's fantastic. I think it's a good club. Good league for him to try and regenerate and revive his career -- and I will say I don't think his career was by any means dead and buried."