'His family have been overwhelmed by the level of support and good wishes but continue to request privacy as this will be vital during this next stage of recovery'.
The 76-year-old Scot was United manager from 1986 to 2013, winning the Champions League twice, the Premier League 13 times and five FA Cups. United had earlier revealed that Ferguson had undergone the surgery and that he was in intensive care.
However, United thanked the many well wishers, including from the likes of rival managers Arsene Wenger, Pep Guardiola and Jurgen Klopp, who spoke of their admiration for Ferguson.
Lukaku, United's top scorer with 27 goals this season, suffered a foot injury in a league win over Arsenal last month.
"[The club] are positive, they are very positive".
Ferguson famously described his mission upon joining United as knocking Liverpool "off their perch".He duly did so as United overtook Liverpool as the most successful side in English domestic football.
But the respect held for Ferguson was even clear in City's celebrations as fans held up a banner reading: "Football aside get well Fergie". "Everyone at Manchester United sends our very best wishes".