Weir, capped 61 times between 1990 and 2000, went on to raise millions through his My Name’5 Doddie foundation following his diagnosis in 2016.
The lock was given an OBE in 2019 for services to rugby, to MND research and to the Borders community.
In a social media post, the WRU said: “The condolences of all those within Welsh Rugby go to Doddie’s family and loved ones. An inspiration to us and so many others.
Former England hooker Brian Moore said: “Very sorry to hear about the death of Doddie Weir. An outstanding man in every sense and one who will be sorely missed. RIP Big Man.”
❤️ The condolences of all those within Welsh Rugby go to Doddie’s family and loved ones.
An inspiration to us and so many others. https://t.co/LwDJt3D6JZ
— Welsh Rugby Union 🏴 (@WelshRugbyUnion) November 26, 2022
World Rugby added: “He leaves an incredible legacy and will be missed by so many in the rugby family and the MND community,” while Wales head coach Wayne Pivac said: “On behalf of the Welsh rugby team, we’d like to send our condolences to Doddie Weir’s family and friends.”
“I hope his family never forget how much he was loved.” wrote TV presenter Dan Walker.
His former club Newcastle paid a moving tribute to the second row who helped the Falcons ascend into the top flight and was an instrumental part of the squad which lifted the 1997-98 Premiership title – still the only team to achieve this remarkable feat the first season after promotion.
“The Scotland and British & Irish Lions lock captained the Falcons in their victorious 2001 Tetley’s Bitter Cup final at Twickenham, and even after his departure from the club in 2002 he remained a regular presence at Kingston Park Stadium,” a statement from the club said.
“Following his diagnosis of motor neurone disease in 2017 Doddie showed his characteristic mixture of determination and good humour in raising many millions for research into the currently-incurable condition.
“It was our honour to display his foundation’s logo on the front of our shirts when we played at St James’ Park in front of a club record crowd of more than 30,000 in 2018, and to play our part in supporting their incredible fundraising activity.
“All associated with Newcastle Falcons would like to express our sadness at hearing the news of Doddie’s passing, whilst at the same time remembering the many happy memories and good times of which he was a central part.”