Tiger Woods' girlfriend Lindsey Vonn fears he will cheat on her

The one thing that
Lindsey Vonn at the 2010 Arthur Ashe kids Tennis day in New York
Lindsey Vonn says could end her relationship
with Tiger Woods is sex with his ex-wife, Elin Nordegren, according to UPI.

While the duo basks in the glow of being  the hottest power couple in sports, Vonn reportedly fears there's one thing that could break them up: sex with his ex.

Tiger Woods and Lindsey Vonn made headlines in March when they announced they were a couple. Vonn is apparently afraid Woods will cheat on her with ex-wife Elin Nordegren during a summer vacation with her and their kids in Sweden, according to  reports.

Nordegren has apparently given her blessing to the couple before and Vonn has been spotted with their children.

Nonetheless, Vonn says that she does not think Nordegren would be above breaking up their relationship behind her back to get back at her ex-husband.

“Lindsey is convinced that Tiger still has feelings for Elin and, if he got the chance, he would dump Lindsey in a flash and get back together with her,” a source said.

Whos is Lindsey Vonn?

Lindsey Caroline Vonn is an American World Cup alpine ski racer who competed with the United States Ski Team. She has won four overall World Cup championships – one of only two female skiers to do so, along with Annemarie Moser-Pröll – with three consecutive titles in 2008, 2009, and 2010, plus another in 2012.

Vonn won the gold medal in downhill at the 2010 Winter Olympics, the first ever in the event for an American woman. She has also won six consecutive World Cup season titles in the downhill discipline (2008–2013), four consecutive titles in Super G (2009–2012), and three consecutive titles in the combined (2010–2012). Vonn is one of six women to have won World Cup races in all five disciplines of alpine skiing – downhill, super G, giant slalom, slalom, and super combined – and has won 59 World Cup races in her career through the end of the 2013 Alpine Skiing World Cup.

Only two ski racers have more World Cup victories in their careers, Annemarie Moser-Pröll of Austria with 62 and Ingemar Stenmark of Sweden with 86. With her Olympic gold and bronze medals, two World Championship gold medals in 2009 (plus three silver medals in 2007 / 2011), and four overall World Cup titles, Vonn has become the most successful American skier in history. Vonn received the Laureus World Sports Awards Sportswoman of the Year for 2010.  She was also honored again as the USOC's sportswoman of the year for 2010.