Jones underwent the same routine medical testing as all replacement players joining the tour and it led to the team's medical staff requesting a further examination by an independent neurosurgeon. This was due to a concern over the players' recent medical history that included two significant knocks to the head while playing for Wales during the recent tour to North America.
On the advice of the neurosurgeon it was determined that it was not safe for Jones to undertake any physical contact for a mandatory three weeks. This is in line with IRB Regulation 10.1 on concussion.
It is anticipated Jones will fly out of Cape Town latr today. Head Coach Ian McGeechan has stated that at this stage no further replacement player will be required.
The Welsh Rugby Union has expressed its disappointment on behalf of the Wales captain Ryan Jones who has been ruled out of the British and Irish Lions tour of South Africa on medical grounds.
A series of medical examinations in South Africa have confirmed that Jones will not be available to play within the time frame required by the British and Irish Lions who face another six games before the tour ends on July the 4th.
Ryan Jones was initially examined by the Wales squad medical team in the USA and was passed fit to travel home to the UK.
A full medical examination of the player was due to take place in the UK late this week but the routine tests were then scheduled for South Africa when he flew out on Tuesday.
A WRU spokesman said: "We fully understand the reasons this step has been taken, but we understand how desperately sad it is for Ryan who was looking forward to the honour of representing the Lions.
"All players know it is important for medical advice to be followed and now he will be able to rest before taking a full part in pre-season training.
"We look forward to seeing him fit and ready for the start of next season."
Ryan Jones said: "I am very disappointed that on medical grounds I have been told that I am not currently fit enough to play an active role on the tour.
"I was looking forward to getting involved with the rest of the lads, but I guess it wasn't meant to be. It has been an up and down year for me in many ways.
"I feel OK at present, but obviously I have to listen to the neurosurgeon's advice in terms of my health and to ensure I make a full recovery."