Foster recently ended his self-imposed international exile, two years after calling time on his England career, and is set to earn a place in Roy Hodgson's squad for the upcoming World Cup qualifiers against Montenegro and San Marino.
Foster's recent performances for the Baggies have been excellent and he is even being tipped in some quarters to usurp Manchester City's Joe Hart as England's number one.
Routledge knows just how big a barrier the former Manchester United and Birmingham man will be to Swansea's hopes of victory.
He said: "He is a very good keeper, some of the saves he made against Chelsea the other day were just world class.
"He is more than capable of performances like that and he is up there with the best, he is a top quality goalkeeper.
"If he wants to go back to play for England he more than deserves a place in that squad.
"We know it is going to be very tough this weekend. They have played some good football at home, we got a few early goals when we beat them here but this will be very different.
"We are in a battle against each other in the league, so it would be nice to come away with something."
Like Foster, Routledge has also enjoyed an excellent season, revelling in the freedom afforded him by Michael Laudrup.
The former Tottenham and Newcastle man has proved particularly effective as part of a rotating trio, along with Nathan Dyer and Pablo Hernandez, behind Michu.
And the 28-year-old admits he has found it easy to slot in alongside the pair.
"We're all capable of nice neat touches, beating a player, finding the final pass and, this season, scoring goals," he said.
"It's a hard role playing in the middle, but you can rotate and most of the time be fresh when you get the ball.
"That works so well at the moment. I think we're all comfortable playing in whatever role the manager picks us in.
"If you see it on the pitch, you'll see Nathan go out to the left, you'll see me go out to the right and Pablo in the middle. We literally rotate constantly."
England number two Ray Lewington has kept an eye on Routledge's progress, but the winger remained coy when questioned on the possibility of his own international prospects.
He said: "It's a nice boost, but my only priority is playing well for Swansea. That's all I'm concentrating on and anything else is an added bonus.
"I know Ray from when I was younger at Crystal Palace and also from Fulham a little bit. He was always in charge of the reserves while I was with the youngsters."
Routledge has had a nomadic career, playing for nine different clubs.
But he now feels settled in Swansea, and recently agreed an extension to his contract.
"It's the first time I think I've signed another contract at a club and it was obviously really nice to get offered it," he said.
"I'm just looking forward to the future now and playing as much as I can.
"Everyone wants to be settled and happy, but the reality is it's not as easy as that. This is the most settled I've been in my career apart from when I first started."
Routledge is one of a number of players to have extended his contract at Swansea this season, and defender Angel Rangel has become the latest after agreeing a new three-year deal to take him through to 2016.
The Spaniard said: "I am settled here, I am enjoying my football, I have married a Welsh girl and I'm building a house in Swansea - I feel like a Welshman now.
"I am very happy on a personal and professional level."