The 19-year-old centre-back has made one substitute appearance for the Saints in the Premier League and is captain of the club's under-21 side.
He led Southampton to victory in last season's Premier League Under-21 Cup.
"Our last two games haven't reached our high standards defensively and he's a new option who adds competition," said Wycombe boss Gareth Ainsworth.
"Jason's a very highly-rated defender who's had good experience in the under-21s at Southampton and they feel he's ready to go out and get a taste of what senior football is like at League Two level," Ainsworth added to the club website.

The 75-year-old was rumoured to be favourite to perform the duty which has previously been carried out by other sporting greats such as Muhammad Ali and Cathy Freeman.
The three-time World Cup winner has been suffering from muscle pains and had hip surgery earlier this year.
"I'm not in physical condition to take part in the opening ceremony," he said.
Coverage of Friday's opening ceremony at Rio's Maracana Stadium begins at 23:35 BST on BBC One.
The problem is that if he sits in a chair you need a winch to get him out of it
Pele added: "Only God is more important than my health. In my life, I've had fractures, surgeries, pain, hospital stays, victories and defeats. And I've always respected those who admire me."
The former Santos player added that it was his "own decision".
Pele's spokesman Pepito Fornos added: "He is walking with a cane. The problem is that if he sits in a chair you need a winch to get him out of it.
"His doctor thought it best that he continues physiotherapy, that he rests and we hope that he will be able to appear at the [Olympic] closing ceremony."
Earlier this week, Pele said he was asked to light the cauldron by the organisers, however he had "an international commitment with an English company". The former footballer added that if he could change his travel plans it would be an "honour" to carry out the task.
In June, Pele was awarded the Olympic Order by the International Olympic Committee (IOC) - the movement's highest honour.
He was named "Athlete of the  century" by the IOC in 1999 despite never competing at a Games because professional players were barred from doing so during his playing days.
Pele, who won his first World Cup winner's medal at the age of 17, is regarded by many as the greatest footballer of all time.
Since retiring in 1977, he has taken up ambassadorial roles both in and outside football, and was involved in politics as minister of sport in his home country for a three-year period from 1995.
And in 2012 Pele was awarded an honorary degree from the University of Edinburgh for his "significant contribution to humanitarian and environmental causes", having worked as a United Nations ambassador for ecology and the environment.
Earlier on Friday, hundreds of demonstrators blocked roads in Copacabana - protesting against the government and the cost of hosting the event - which resulted in a change of route for the Olympic torch relay.
The Olympic torch began its final journey to the Maracana beneath the iconic Christ the Redeemer statue that overlooks Rio.
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Wycombe Wanderers have signed teenage Southampton defender Jason McCarthy on an initial one-month loan.
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Brazil football legend Pele will not light the Olympic cauldron at Friday's opening ceremony in Rio.