Sir Alex Ferguson has extended his deepest sympathy to the family of Liam Miller who died on Friday at the age of 36.
Miller - whose former clubs included Celtic, Manchester United and Hibernian - was diagnosed with pancreatic cancer last year and had been undergoing treatment in the United States and Ireland.
Sir Alex, who signed the Republic of Ireland midfielder for United in 2004, said: "I am very sad to hear that Liam has died.
"He was a good professional, who served our club in an excellent manner. He was a quiet, unassuming young man and was popular with everyone at Carrington.
"On behalf of all my staff who worked with Liam at the time, we send our deepest sympathy to his family."
Celtic held a minute's silence in honour of Miller ahead of their Scottish Cup fifth round win over Partick Thistle.
Instagram
This content is provided by Instagram, which may be using cookies and other technologies.
To show you this content, we need your permission to use cookies.
You can use the buttons below to amend your preferences to enable Instagram cookies or to allow those cookies just once.
You can change your settings at any time via the Privacy Options.
Unfortunately we have been unable to verify if you have consented to Instagram cookies.
To view this content you can use the button below to allow Instagram cookies for this session only.
Meanwhile, Manchester United will wear black armbands in Miller's memory for Sunday's televised clash against Newcastle at St James' Park.
The Football Association of Ireland have also confirmed there will be a minute's silence ahead of the President's Cup tie between Dundalk and Miller's hometown club Cork City on Sunday.
Twitter
This content is provided by Twitter, which may be using cookies and other technologies.
To show you this content, we need your permission to use cookies.
You can use the buttons below to amend your preferences to enable Twitter cookies or to allow those cookies just once.
You can change your settings at any time via the Privacy Options.
Unfortunately we have been unable to verify if you have consented to Twitter cookies.
To view this content you can use the button below to allow Twitter cookies for this session only.
Twitter
This content is provided by Twitter, which may be using cookies and other technologies.
To show you this content, we need your permission to use cookies.
You can use the buttons below to amend your preferences to enable Twitter cookies or to allow those cookies just once.
You can change your settings at any time via the Privacy Options.
Unfortunately we have been unable to verify if you have consented to Twitter cookies.
To view this content you can use the button below to allow Twitter cookies for this session only.