Referee Oliver did not point to the spot despite animated appeals from Alli and Co. Highlights showed Walker making a slight movement of his arm to touch the ball away from the Tottenham midfielder.
"I thought it was a penalty but we didn't get it. In that action it is not that confusing. Michael Oliver was standing behind watching," he told beIN SPORTS.
"When it is not clear, it is not clear but this action is more than clear. Both players fighting for the ball inside the box and Michael Oliver was in a fantastic position to see what was going on there.
"For me and maybe not for Manchester City but for me and for the rest of humanity I think yes it was a penalty."