Wilkinson, currently touring Japan with Newcastle Falcons, was admitted to hospital after complaining of feeling unwell.
The 26-year-old is on medication to counter the inflammation and will continue to be monitored.
The Falcons are due to play their first tour match against NEC Green Rockets in Tokyo on Saturday before taking on Toyota Verblitz in Toyota City, near Nagoya, on Tuesday.
Wilkinson was hoping to re-establish himself with Newcastle and England this coming season after an injury-ravaged two years and a disappointing summer tour with the British & Irish Lions.
He has suffered a catalogue of injuries since winning the World Cup in November 2003 and has not played for England since.
A serious neck and shoulder injury has been his most serious concern but he has also had arm and knee problems. His injuries prevented him from taking up the England captaincy after the retirement of Martin Johnson.
His appearances for Newcastle have been limited in recent seasons but he was given extra time to prove his fitness for the Lions tour of New Zealand.
Wilkinson came in for some criticism after his performance at centre in the first Test and was moved to his natural fly-half position for the second match. He missed the third Test through injury.