The 1-0 loss means Milan are still to gain a point in their group.
"Clearly, incidents can decide a result, but our performance was not good today. Our opponents did better, were sharper, more precise, had more intensity," Pioli told Mediaset.
“We didn't start well, didn't hold the ball well and didn't create enough chances. The team was balanced and competitive, but the performance was not the best and at this level if you aren't sharp both attacking and defending, you will suffer. Porto did better than we did."
He added: “We must believe. It's easier to say than do, but the other two teams are four points ahead of us. Unfortunately, this was the game we really shouldn't have played this badly, of all of them, but we have to just keep going.
“I have to find out why we weren't sharp or precise enough this evening. I don't want to talk about the referee. I have other things to focus on."
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!