Ally McCoist's side got their tour of North America off to a disappointing start as they turned in a below-par performance in California to leave the boss with plenty of work to do ahead of the SPFL Championship campaign.
The Light Blues will return to action on Saturday when they face Sacramento Republic before heading to Canada for a further two friendly fixtures and facing Derby just days before their first competitive clash of the season against Hibernian on August 5.
The plastic pitch at Ventura College, complete with American football markings, was hardly ideal for the Gers but Foster insists that shouldn't mask their deficiencies on a poor night for the champions.
He said: "I think the only thing we can take from it is the fitness aspect of the game.
"There were a lot of bits and pieces that weren't great and that is something that we will look at.
"We tried a new formation in the first half and it will take a bit of time to get used to it. But I think the only thing we can take from it is fitness.
"They looked hungry and sharp and moved the ball really well. They caused us a few problems and were quick all over the pitch.
"I think you can see that they are a few games ahead of us in that respect.
"[The pitch] slowed the ball down if you were trying to break quickly.
"If the ball was on the ground, it didn't move as quickly as normal.
"That is not an excuse. There were a few passes that, even on grass, would have been misplaced.
"It was tricky and the bounce and things like that are always difficult on a synthetic pitch.
"But that is not something we are going to use as an excuse."
One of the few positives for McCoist was the fact that many of his first-team stars got vital match minutes under their belt on a night where he handed starts to summer signings Darren McGregor, Marius Zaliukas and Kenny Miller.
Defender Bilel Mohsni got the only goal for the Gers as the hosts ran out comfortable winners on a night where the defending was far from good enough.
And Foster admits the 5-4-1 formation that McCoist tried out for the first time needs a lot more work on the training field in the coming days and weeks.
"I got to play a bit higher up," the ex-Aberdeen man told RangersTV.
"It does take a bit of getting used to. Usually me and Lee Wallace or the full-backs are coming from deeper and you tend to time your runs a bit more as opposed to being that high up the pitch.
"This was the first time we have tried it. We worked on it in training and I am sure we will work on it a lot more.
"I like going forward. As a full-back that is the most enjoyable part of the game. The worst thing is having to defend.
"I like pushing forward and trying to get crosses into the box and create chances. In that respect, it was a good formation for me."