Demi Lovato's estranged father is facing a dangerous surgery to remove a tumor in his throat and he's heartbroken over the fact that his daughter refuses to speak to him.

Patrick Lovato spoke exclusively to RadarOnline.com, pleading for his youngest daughter to give him a call.

"Demi and I haven't spoken in so long and all I want her to do is call her daddy," Patrick tearfully said.

Disney star Demi Lovato proved she is firmly on the road to recovery when she took to the field at the World Series game in Arlington, Texas on Monday to sing the national anthem, and RadarOnline.com has video of her impressive performance.

The recently rehabbed teen nailed the patriotic song as she belted out the Star-Spangled Banner in front of hundreds of baseball fans (and millions of television viewers) at the Game 5 face-off between the Texas Rangers and the St. Louis Cardinals in her home state of Texas.

Dressed in a red Texas Rangers shirt with matching black shorts and blazer, Demi showed no sign of the nerves during her big-voiced performance, but she admitted to her Twitter followers on Sunday that she had baseball-induced butterflies.

Demi Lovato’s ailing father has a heartbreaking message for his estranged daughter: please call me.

Patrick Lovato exclusively told RadarOnline.com that he has been desperately trying to reach his 19-year-old Disney star daughter, but so far to no avail.

EXCLUSIVE PHOTOS: Demi Lovato’s Childhood Pics

Demi Lovato is getting a Christmas break from rehab, RadarOnline.com has learned exclusively.

PHOTOS:  Demi Lovato Flashes Her Cleavage In Racy New Pics

The troubled Disney star is being permitted to spend "Christmas with her family outside of the facility," a source close to the situation tells RadarOnline.com exclusively.  "She will return to the treatment center that night."

Demi has been in rehab since last month, following her Halloween weekend meltdown when she punched back-up dancer Alex Welch.  At the time Lovato was out on tour with the Jonas Brothers.

PHOTOS:  Demi Lovato In A Teal Bikini

Demi went into treatment, her rep said, because of "emotional and physical issues she's dealt with for some time."

Since then, RadarOnline.com has reported on the teen's history of "cutting" and posing for racy photos with other girls.

PHOTOS:  Demi Lovato Shows Signs Of Cutting Going Back To 2008

But it looks like she's making a turn-around.  RadarOnline.com has learned Demi is up for a role in the new Avengers movie that will start shooting April 1.

PHOTOS:  Celebs Who Have Been In Rehab

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Demi Lovato To Spend Thanksgiving In Treatment Center

The dancer Demi Lovato allegedly punched in the face is seeking medical treatment from a plastic surgeon and is taking action against the Disney star in a lawsuit which will be filed next week, RadarOnline.com has learned exclusively.

PHOTOS: Celebs Who Have Been In Rehab

Alex Welch's high-powered attorney, Donald Karpel, says that the injuries his client sustained warranted emergency medical care and further consultation from a cosmetic surgeon.  Karpel also says Welch intends to take Lovato to court.

Demi Lovato's dad has a few words of warning for the girl allegedly hit by his famous child: "don't sue my daughter, you won't win!"

PHOTOS: Hollywood's Hottest Child Stars Grow Up And Strip Down Into Bikinis!

The Disney star, who has been in a treatment center since October following an incident with another girl on tour with the Jonas Brothers, may become the target of legal action, but her father told RadarOnline.com that Demi shouldn't be concerned about the threat of legal action.

Demi Lovato will be spending the upcoming Thanksgiving holiday at her treatment facility.

PHOTOS: Stars Who Have Been In Rehab

The singer and actress, who has been at the facility for over two weeks, will be joined by her family.

PHOTOS: Demi Lovato Sports A Teal Bikini

They will be there “to celebrate” with Lovato, her rep told People.

The rep added:  "She remains committed first and foremost to her treatment. Demi has made tremendous progress to date, but understands that she has more work to do."

Demi Lovato is in her second week at a treatment center working on “emotional and physical issues” and is doing well according to her father Patrick Lovato, who recently spoke to the young star over the phone.

In an exclusive interview with RadarOnline.com, Patrick said: “Demi’s doing great, she’s such a strong girl.”

EXCLUSIVE PHOTOS: Before Demi Was Famous

Patrick said Demi called him this week and they spoke about his cancer. “She told me she loved me, she really loves her daddy,” he said.

“She told me she’s getting better.”

PHOTOS: Demi Lovato With Signs Of Cutting

Before she struggled with emotional and physical issues, teen sensation Demi Lovato was an adorable youngster, and only RadarOnline.com can take you inside her childhood photo album.

EXCLUSIVE PHOTOS: Demi Lovato - Before She Was Famous

"Demi was the most lovable child ever," her father, Patrick, told RadarOnline.com. "She and her sister Dallas did nothing but laugh and have fun all the time."