Foster has not made an appearance for United since his man-of-the-match performance in the Carling Cup final win over Tottenham almost a month ago.
Under the circumstances, it was a major surprise for the 25-year-old to be selected in Fabio Capello's squad for England's friendly encounter with Slovakia on Saturday, which acts as a warm-up for the key World Cup qualifier against Ukraine at Wembley on April 1.
And Foster is acutely aware he will only stay in Capello's plans for South Africa 2010 if he can secure more first-team action for United.
It is not an easy situation, made harder by the fact that in Edwin van der Sar, Foster has a pretty difficult rival to displace, the Dutchman having recorded a record 14 successive clean sheets this season.
"You can't really go knocking on the manager's door when the goalkeeper in front of you is doing that," said Foster.
"Edwin is one of the coolest, calmest goalkeepers I have ever met. He is very laid back and that calmness spreads through the team.
"You can see how comfortable the defenders are about giving him the ball at his feet."
The appreciation of Van der Sar as a team-mate is obvious, but there is no sense of inferiority from Foster.
Given none of the other seven goalkeepers Capello has previously selected are at a top four club, the chances are Foster faces a harder time getting into the United side than he does with England.
Like Van der Sar, Chelsea's Petr Cech, Liverpool's Pepe Reina and Arsenal's Manuel Almunia are rated among the best in Europe and represent the standard Foster must reach.
"You are talking about Manchester United," he said. "They are the best team in the world and you have got to be up to the job.
"I am sure that if I got a chance and I was not doing my job I would be taken out of the side.
"But I do feel I am up to it. I train with the best players every day and I hold my own. I am definitely up for the challenge."
As Capello has pledged to make his maximum six substitutions on Saturday, Foster has a decent chance of being involved, even if Robert Green, who was part of the squad beaten by Spain last month, has more of a claim.
Capello also has to solve the conundrum regarding Steven Gerrard's best position and where, if the answer is behind a main striker as has proved the case at Liverpool, that leaves Wayne Rooney.
There is no sense the loss in Seville - from which Gerrard, Rooney and Rio Ferdinand were all absent - has punctured public backing of the Three Lions, which just 8,000 tickets remaining to be sold for the game against Slovakia, hardly the most attractive opposition.
The Slovaks do top a World Cup qualifying group that includes the Czech Republic and they did account for Poland last October.
But England are expected to dominate possession which means, if he does play, Foster will be in a position more akin to United than the two years he spent with Watford.
"You can watch any United game and sometimes the keeper isn't touching the ball for 30 minutes at a time," he said.
"My two years with Watford were completely different, especially my second season when it was pretty much backs to the wall in each game.
"You know that you're going to have a lot to do and that at any given second you can have a shot to deal with.
"Keeping your concentration when you are not as busy is something that only comes with experience and games."
Should he win a second cap this weekend, adding to the first he won against Spain under Steve McClaren in February 2007, it would be another important milestone for Foster, who has vowed to renew his efforts next season in order to achieve his dream double.
"The biggest club in the world against the biggest competition in the world, that is the dilemma," he said.
"Playing for England is a hugely important thing but I am also at the biggest club in the world. I will only get one chance at that and I don't want to give it up.
"I have to come back next season and get into the manager's face as much as I can. I want to be playing and I want to get into the World Cup squad next season."