Sir Alex Ferguson was among the mourners gathering to pay their respects to former Celtic captain and manager Billy McNeill.
McNeill's funeral is being held at a church in Glasgow city centre before the cortege makes its way to Celtic Park, where thousands of supporters are expected to pay tribute.
McNeill's body was taken to St Aloysius Church on Thursday evening ahead of a service at 11.30am on Friday morning.
Some streets in the city centre and east end of Glasgow will be closed, with fans expected to line the pavements to pay respect.
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Former Rangers striker Ferguson was among those to arrive at Celtic Park, where buses were waiting to transport mourners to the church.
Ex-Rangers managers Walter Smith and John Greig and former Celtic players Frank McGarvey, Frank McAvennie and Tom Boyd arrived at a similar time.
McNeill, who won 31 trophies as player and manager for Celtic, died last week aged 79 after suffering from dementia in recent years.
In a statement earlier this week, McNeill's five children extended an open invite to fans to pay their respects.
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They wrote: "The love and affection shown towards our father is nothing short of amazing.
"Our father always made time for the fans and knew how important they are so we would like to send an open invite to help us pay our respects to him.
"His body will be taken into St Aloysius Church on Thursday evening at 6.30pm, with the church staying open for a short while after the service."
Former Celtic managers Brendan Rodgers, Martin O'Neill, Gordon Strachan and Kenny Dalglish left for the funeral on buses from Celtic Park.
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McNeill's fellow Lisbon Lions such Bobby Lennox, John Clark, Jim Craig and Bertie Auld were also present.
The likes of Murdo MacLeod, Tommy Coyne and Pat Bonner - who played under McNeill for Celtic - were also among the mourners.
McNeill also managed Aberdeen and former Dons players Willie Miller and Alex McLeish were there to pay their respects.
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McLeish said outside the church: "I worked with a legend. Billy gave me my debut, I'll never forget that day.
"(He was) brilliant - banter on the training ground, serious when he had to give you a tongue lashing.
"Type of guy who when he walks in the room everyone stands up or shuts up. He was a great man. I know his family well, he'll be sadly missed."
