Jordan Spieth US Open 2015
American Jordan Spieth assumed the role of favorite heading into the British Open next week at St. Andrew's in Scotland. Getty Images

Following No. 1 Rory McIlory’s ankle injury and withdrawal, American Jordan Spieth assumes the frontrunner position ahead of next week’s British Open at St. Andrew’s in Scotland.

The 21-year-old Spieth, who’s a threat to clinch the modern Grand Slam after claiming the Masters and U.S. Open this year, saw his odds improve from 5/1 prior to McIlory’s announcement to 9/2 on Thursday.

Spieth has played at St. Andrew’s twice before, firing off a 10-over par back in 2013 but improving to two-under for 36th place last year, yet this go-round he’s a far stronger and improved player. He fired off a record 28 birdies at Augusta and nearly eclipsed Tiger Woods record of 18-under through four rounds, and then Spieth overcame a harrowing Chambers Bay course to claim the U.S. title by a single stroke ahead of a far more experienced field.

Though the site was still a bit pessimistic, FiveThirtyEight said Spieth’s chances of notching golf’s first Grand Slam improved by 33 percent, after McIlory went down but they still aren’t strong overall at 1.1 percent. But according to Sportsbook.ag, Spieth's Grand Slam chances currently sits at 20/1.

After Spieth, odds makers haven’t shifted the rest of the field’s chances much. Dustin Johnson, who endured a heartbreaking runner-up finish to Spieth at the U.S., holds steady at 12/1 and so does England’s Justin Rose at 16/1 and Australia’s Adam Scott at 18/1.

However, Tiger Woods did jump from 22/1 to 20/1. The three-time Open champ, last victorious in 2006, bounced back from missing the cut at Chambers Bay to finished in 32nd place at the Greenbrier Classic last week and talk has once again heated up over another potential comeback from Woods.

Check out the last odds below.

Odds to Win the British Open

Jordan Spieth 9/2

Dustin Johnson 12/1

Justin Rose 16/1

Adam Scott 18/1

Henrik Stenson 20/1

Louis Oosthuizen 20/1

Tiger Woods 20/1

Jason Day 25/1

Martin Kaymer 25/1

Phil Mickelson 25/1

Rickie Fowler 25/1

Sergio Garcia 25/1

Bubba Watson 28/1

Paul Casey 28/1

Hideki Matsuyama 33/1

Patrick Reed 40/1

Shane Lowry 40/1

The full list of odds can be viewed at Bovada.lv.