LOUISVILLE, Ky. — Preakness winner Rachel Alexandra worked a half mile at Churchill Downs, but the filly's owner says it may be another week before he decides whether to enter her in the Belmont Stakes.

Jess Jackson said Monday that Rachel Alexandra is "progressing well" and will work again next week before a decision is made on the third leg of the Triple Crown on June 6.

Jackson and Harold McCormick bought Rachel Alexandra after she won the Kentucky Oaks by 20¼ lengths May 1. She became the first filly in 85 years to win the Preakness on May 16, with jockey Calvin Borel guiding her to victory over Kentucky Derby winner Mine That Bird.

"She's recovering nicely and I think, for the time that's elapsed, only nine days, she's right on — but we can't make a decision until we know," said Jackson, who owns Stonestreet Stable. "My concern is her attitude. She thinks she can run through a brick wall, so her attitude has to be monitored. If anything, we have to hold her back a little bit because she's so eager to run."

Rachel Alexandra worked the half mile in 50.20 seconds under exercise rider Dominic Terry over a sloppy track. Also, Mine That Bird worked the same distance in 51 seconds under Borel.

If Rachel Alexandra does not run in the Belmont, which would give her a shot at becoming the first filly to win two-thirds of the Triple Crown, Jackson said the Mother Goose Stakes for fillies at Belmont Park on June 27 is an option.

"It might not be as soon as you'd want but we're still considering the Belmont," Jackson said. "The Mother Goose would give her a little extra time if she needs it. The Belmont would be a full (effort) for her right now."

With the no-decision, Mine That Bird trainer Chip Woolley also gave Borel more time to decide which horse he'll ride in the Belmont. Woolley had set a Monday deadline for the jockey.

"He won me a Derby, he deserves the time it takes for him to make the conscious, right decision," Woolley said. "And nobody knows really if that filly's going to be running in the Belmont, so it could work out where that's not even a decision for him. I think a little bit of time's not too much to ask."

If Borel chooses Mine That Bird, then Jackson will go with Robby Albarado if the filly runs in the Belmont.

"Calvin is a great jockey and I hope he'd be willing to go with her," Jackson said. "He has to make his decision for himself and if we're in there together and he's not on our horse it'll probably be Robby Albarado, who was with us with Curlin."

Albarado is one of the top riders used by Steve Asmussen, who took over as the filly's trainer after the horse was sold.

Jackson said Rachel Alexandra will give him a sign whether or not the Belmont is next.

"We have to monitor her and make sure that we preserve her because she's so special; the principal concern is the horse herself keeping her sound and letting the public enjoy her," he said. "It's not necessary that she go in the Belmont, she's got a whole season ahead. She's been running the whole year so we have to monitor that very carefully."