Walker briefly lost his place in the Manchester City starting eleven during an eleven-game spell between February and April, when he started just three times.
At the time Guardiola said Walker did not have the requirements to play in his new defensive system.
Guardiola rather deployed John Stones in an inverted full back position which requires the former Everton defender to drift inside to join Rodri in midfield.
However an injury to Nathaniel Ake forced Guardiola to reschuffle his backline, allowing Walker to regain his place in the side.
Walker has responded with some impressive performances lately, including coping with the threat of Real Madrid dangerman Vinicius Junior during a Champions League semi-final tie at the Santiago Bernabeu last week.
It was Guardiola who signed Walker from Tottenham Hotspurs in 2017 but the England international did not hide his feelings when asked about his recent snub.
"I have to react as a professional, he is my manager, my boss, sometimes some opinions in football you don’t always agree with but what he has done for me and Man City has been nothing short of tremendous", Walker said ahead of the return leg against Real Madrid at the Etihad Stadium on Wednesday.
"Did it hurt? Of course it did. You start to doubt yourself but you have to go back to basics to what he bought you for and prove him wrong and that is what I have done. I am one of the captains, have to make sure my disappointment isn’t shown."
Walker has made 33 appearances for Manchester City this season.
