I think you'll ulimately need peroxide to remove that. Sometimes you get you can get lucky and it will come out with a general purpose spotter and extraction...but I doubt it will work if that's a cellulose fiber.
A few warnings:
1. You could end up overwhitening the area that you treat with the peroxide. Make sure you have in writing that you can't be responsible for any color difference. I know that "a little whiter and brighter" will be a 100% improvement over the existing stain, but I just helped a cleaner avoid paying a 16,000.00 claim after removing a urine stain from a similar fabric.
2. If you go with anything stronger than 3% peroxide, and the fabric is has cellulose fibers in it (probably does), it may weaken them. It might not show up for a while, but if they sit on it and it splits in the same place the stain came out, they'll remember you treated it.
This message of fear, doom and gloom was provided at no charge from your friendly, battle scarred, and cynical curmudgeon.