The All Blacks play the Pacific islanders at Eden Park as an opportunity to test some combinations ahead of the three-test series against Warren Gatland's British and Irish Lions, starting on June 24.
Coles has been the major injury concern for both the Wellington Hurricanes and the All Blacks with knee and calf problems and concussion symptoms keeping him out of action since March 18.
Flyhalf Aaron Cruden (knee) and Ryan Crotty (ribs) are also concerns, while captain Kieran Read and fellow loose forwards Jerome Kaino and Liam Squire are returning from layoffs following surgery.
Read has already ruled himself out of the Samoa game, but has said there would be no issues with his match fitness.
The 31-year-old missed the first six games of Super Rugby as he recovered from wrist surgery and then broke his thumb while making a tackle in his third game back.
"People are trending upwards, and we're excited about that," Foster told reporters in Auckland.
"All the information we have on the injured group is pretty positive now, and by the end of the week we'll have a good handle on who's ready to go either Friday or next week."
Coles was yet to take part in any training involving contact, but Foster said he had shown steady improvement.
"He... is still working with the doc and physio and doing his own thing," Foster said. "Once the medicos have given the all-clear... but they're delighted with his progress.
"The fact I used the word 'delighted' means we're delighted with progress, so I wouldn't say it is the same old."
Foster added there were no concerns about facing a physical Samoan side before they meet the Lions at the same venue eight days later.
"I know everyone is talking about the big battle around the corner, but our mentality is the best way to prepare for a battle is to have a battle," said Foster.
"The fact we're playing Samoa at Eden Park, and there is a big Samoan community here, means it's going to be a significant game.
"Last time we played them they pushed us to the wire in Apia. Rest assured this will be a full-on battle and we think that's the best way to prepare for anything."
(Reporting by Greg Stutchbury in Wellington; Editing by Sudipto Ganguly)
