The Saints face a very tricky test at the Etihad Stadium against a City side who have yet to suffer defeat in all competitions this season. However, Mauricio Pellegrino's men are coming off the back of a 4-1 win against Everton at St Mary's on Sunday.
Walker and Bertrand go a long way back having played together in the England set-up whilst also coming up against eachother in both the Premier League and Football League.
"Ryan’s a year older than me but we came through the England youth set up together and we go quite far back,” said Walker.
“The earliest memory of Ryan I have is when I played against him for Sheffield United when he was with Reading, I think it was about eight years ago. He’s a top left-back and you don’t win the Champions League if you’re just an average player."
Walker an admirer of talented Bertrand
The 28-year-old Southampton winger won the Champions League during his time with Chelsea, but Walker was pleased that he left Stamford Bridge in order to get more gametime.
“He left Chelsea to go and play regular football and that’s what he needed to do.
“It says a lot about him as a person that he didn’t want to only play every now and then for Chelsea and I think he’s shown at Southampton what a talent he is.” Walker added.
The pair have represented England a substantial amount of times over the previous few years with Walker earning 32 international caps and Bertrand 19 - something they'll both look to add to at the FIFA World Cup this summer in Russia.
City will be hoping to maintain or extend their gap at the top of the league on Wednesday as they currently have an eight-point margain over city rivals Manchester United after a comeback win at Huddersfield Town on Sunday.