The 76-year-old is regarded as Britain's most successful football manager, according to the BBC.
During this time the club was 13 times champion of England and twice won the Champions League.
I, together with the whole fraternity of football managers in the LMA, wish him well and hope for a speedy recovery from his surgery.
On Instagram, with a picture of him as a youngster alongside Ferguson, Beckham wrote: "Keep fighting Boss".
He managed Manchester United between 1986 and 2013.
Absolutely devastated to hear about Sir Alex being unwell in hospital.
Fittingly, Ferguson's treatment and recovery will be carried out near to the place where he masterminded the rebuilding of United. "Thoughts with all the family". Meanwhile, Ferguson's family have requested privacy as he recovers in Salford Royal Hospital. The children of players and staff who played and worked under him still receive birthday and Christmas presents from Ferguson and his wife Cathy.
The outpouring of love and support from so many men who played under Sir Alex through his time at United just serves to highlight how important a figure he has been in so many footballing lives.
Peel Hunt Reaffirms Purchase Rating for YouGov (YOU)
Total analysts of 2 have positions in Harworth Group (LON:HWG) as follows: 2 rated it a "Buy", 0 with "Sell" and 0 with "Hold". State Board Of Administration Of Florida Retirement Sys invested 0.17% of its portfolio in Prudential plc (LON:PRU).
Many current and former United players, including Michael Carrick, Rio Ferdinand, Diego Forlan and David de Gea also offered messages of support as did United's Premier League rivals Manchester City, Arsenal, Chelsea, Tottenham Hotspur and Liverpool.
"My thoughts and prayers are with you, my dear friend".
The end of Beckham's United career came after a freakish incident in which Ferguson kicked a boot in the player's direction, cutting him over his eye.
He remained a regular visitor to Old Trafford and was there last Sunday to make a presentation to old rival Arsene Wenger on the Arsenal manager's last appearance at the ground before he leaves the London club.
"Hang in there Sir Alex", explained town captain Vincent Kompany, who's won the premierleague three days since 2012. Headway, the brain injury association, said a hemorrhage can be the result of a ruptured aneurysm or a blow to the head, including a minor injury.
"The long-term consequences are quite hard to anticipate", head-way's Luke Griggs said.
FC Barcelona too wishes a speedy recovery for Sir Alex.