The 27-year-old has spent the vast majority of his career at centre-half, but was deployed at right-back when City thrashed Leeds United 7-0 in December and impressed Guardiola with his performance that night.
“He played against Leeds in that position and was brilliant,” Guardiola said at his post-match press conference.
“Today he was more than brilliant. Today he was the most important player that we had. In the final third Joao was brilliant too, but John played really well, against Leeds playing to the back four and today, with three, he was perfect.
“He can play in both positions. He convinced me. He pays attention, he is so clever, strong in the air and his build-up is brilliant, how he commits and drives with the ball. He was really good.”
Watch the full press conference in the video above.