She was rushed to hospital after the accident in the early hours of the morning and after two days of treatment, was allowed home to the couple's mansion in Prestbury.
However, her condition deteriorated and she had to be re-admitted after taking a turn for the worse last Wednesday.
A spokesman for the couple said: "It was a pretty bad smash and Jessica has got a lot of internal swelling and a cracked ankle.
"She has had a series of scans to check for internal bleeding and possible organ damage.
"Stephen is devastated but at the same time grateful it wasn't worse."
A source close to the former Irish international said: "He's totally freaked out and doesn't want to leave her.
"I'm not sure if the police went to the accident scene or not but Jessica is hurt pretty badly."
The couple have a two-year-old son, Jacob, and are renowned for their "bling" lifestyle and their love of the high life.
They flew over here last month for the VIP Awards where they quaffed champagne in the Shelbourne Hotel all night with fellow guests including Katie Price and Claudine Keane.
And Stephen, who has an intricate wing tattoo covering the whole of his back, is car crazy.
Two years ago he bought Jessica a €280,000 customised Bentley convertible for her birthday. Around €1,200 was spent to change the car's winged B logo to Jessica's initials JL.
Then Stephen spent more than €2,000 on red leather seats with the message "To Jess, love from Stephen" stitched on to them and a further €5,000 on bright-red alloy wheel rims with Jessica's initials on them.
The player, who has two children from a previous relationship, has a Range Rover with pink wheels, a €190,000 Lamborghini, a €120,000 Audi R8 and a €88,000 Porsche.