You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
Crotty racked up another concussion in a head clash with midfield partner Jack Goodhue in the Bledisloe Cup opener against Australia.
The 29-year-old has suffered a series of blows to the bonce over the years, including one which required a rest in May during the Crusaders triumphant Super Rugby season.
The latest knock has prompted fans, including Crotty's sister Shea, to question whether he should return to the game.
The onus has gone on the sport in recent years to exhibit more caution around concussion, so players don't end up physically and mentally damaged in later life.
Foster said Crotty would now go through "the protocols" to address the issue.
"There is no pressure on him to come back and play in a hurry.
"The beauty of how we handle it is that we give him the space to recover properly.
"The signs are really positive in the last few days."
Foster said a decision about returning was up to Crotty.
"At the end of the day, his health is our greatest concern.
"The good thing is the decision is in his hands. And I don't think it is up to us or anyone else to decide what he wants to do."
Crotty spoke about his previous head knock in June.
"You rest until there are no symptoms, then you can start to train again and increase the intensity."
He was asked whether he rehabilitated along similar lines to other injuries, like a hamstring ping.
"That's kind of how the doctors set it out.
"You're just as diligent to make sure it's right before you come back and play.
"You know when you're right and when you're not. Once you do feel right, you gradually increase your training load to get back to where you were."
Stephen Kara, the former Blues doctor, now runs a concussion clinic based in St Johns.
He told Radio Sport the symptoms are hard to define.
"They can be wide ranging and varied.
"I think of them as clusters: Is the patient noise or light sensitive? Do they have difficulty concentrating or remembering? Is their head feeling thick and foggy?
"Alternatively, there might be neck-based symptoms that affect balance: Is there dizziness, like being on a rocking boat or feeling the world is moving around you? Or are there emotional-based effects like irritability, frustration, sadness, tearfulness or fatigue?"
Kara said they can access a lot of normative data, but that's only one part of the diagnosis.
"70% of people get better within two weeks from our data, whereas kids take four weeks, but it can be a straight-forward process if you do the right things early.
"One danger to look for are people who take longer to recover each time they get a concussion, as well as those who had less force applied but produce the same symptoms. Those people worry me.
"He [Crotty] will be getting some good advice and there'll be no rush to get him on the field. It comes down to the doctor, coach and player deciding what his future looks like."