Brown was stretchered from the ground in the third term of the Eagles' seven-point loss to Fremantle on Saturday afternoon. The key defender fell awkwardly on his right knee and given his history there were immediate fears for his future.
The 25-year-old missed the entire 2008 season after rupturing the anterior cruciate ligament in his left knee in a practice match against Collingwood in Albany.
Although it is not the same knee Simpson said there were grave concerns for Brown, who will have scans to determine the extent of the damage.
"I went in thinking the worst," Simpson said.
"But there is a little glimmer of hope that it might not be as bad as we thought. But a very small chance."
If the Eagles lose Brown for the rest of the year they may be forced to send Jeremy McGovern back to defence or turn to youngsters Jacob Brennan or Blayne Wilson.
Simpson definitely ruled out any thought of turning to former skipper Glass, who retired last week.
"I saw him at training the other day and he wasn't quite right," Simpson said.
"His ankle was sore and his hip was sore. He looks like an old man on the track already so I don't think we'll be calling on Glassy and I don't think he'll be putting his hand up."
Simpson was both proud and disappointed of his side's performance against Fremantle.
After leading at both quarter-time and half-time, the Eagles were held goalless in the third term to trail by 24 points at the final change.
But West Coast kicked the first four goals of the last quarter to hit the front only for Fremantle to find another gear.
"We just dropped away in that third quarter," Simpson said.
"Their good players stood up and got the ascendency.
"At three-quarter-time we didn't change too much we just attacked the game a little bit more and I thought we saw some really good signs in the last.
"I was really pleased that our players found a bit of grit and it's a really good sign for us for the long run. It's something that's been missing a little bit."
However, goalkicking was a major issue again for West Coast. It is the fifth time this season the Eagles have had more scoring shots than their opponents and lost.
"Having more scoring shots than an opposition and losing, whilst it's not pleasing, it probably says you're doing a lot right," he said.
