Lindsey Vonn is scared Tiger Woods may cheat with his model ex-wife Elin Nordegren---so Lindsey is demanding that she comes along for a family vacation Tiger and Elin have planned with their children.

Tiger Woods was supposed to go to Sweden on a summer trip with his ex-wife and children...but Lindsey Vonn is demanding to come, also. And Elin's not happy about it. Although Elin approves of Lindsay and Tiger as a couple, the three of them stuck together is just too uncomfortable for Elin.

Vonn is convinced that Woods still loves his ex and that "if he got the chance" he'd dump her to get back with Nordegren, sources say.

Woods and Elin Nordegren have been planning the trip for awhile, but at the last minute Lindsey Vonn demanded that she come along.

Ummm....awkward. And obviously, Elin didn't like it.

 "Elin found out what Tiger was planning and told him he can come to Sweden, but not bring Lindsey," a source said.

Vonn, a 28-year-old Olympic skier, and Woods, 37-year-old pro golfer, begin dating a few months ago.

And the thought of Tiger being with his ex in a strange country freaked her out-but Elin's reaction was worse. She said she doesn't want Lindsay spending time with Elin's children.

"It started a huge fight between the women, with Elin saying she doesn't want Lindsey around her kids," the magazine reported,

Woods and Nordegren, 33, were divorced in 2010 after he got caught cheating...so perhaps Vonn being concerned about infidelity is warranted.