The defender insists the USA's superb showings at the World Cup prove his point as Ally McCoist's side gear up for the first of four friendly fixtures across the Atlantic.
The League One champions jetted out Stateside over the weekend and will kick off a packed schedule against Ventura County Fusion tomorrow.
They will then face Sacramento Republic before flying to Canda for matches against Victoria Highlanders and Ottawa Fury.
And Foster insists each will give McCoist's side a stern enough test - regardless of the fact none of the four are MLS outfits - because of the work ethic of North American sides.
He said: "You saw from the USA's efforts at the World Cup that the one thing we'll get from teams there is the work they will put in."
After spending time in the Highlands to kick off their summer schedule, beating Buckie Thistle 3-0 and drawing 1-1 with Brora Rangers, the Ibrox side are stepping up their preparations.
And Foster believes their trip over the pond is just what they need at this stage.
He added: "Their football season runs differently from ours and they'll be in mid- season when we go over there.
"They will give us challenging games in terms of fitness as much as anything and that's ideal."