The former striker and fans' favourite, who played 126 times for Burnley FC between 1960 and 1968, was injured after he fell down the stairs on Tuesday night at his home in Burnley.
The 75-year-old, who is married to Rita and has three sons, remains in the high dependency unit at Royal Preston Hospital having suffered a fractured skull and broken bones.
His family are hoping for a full recovery. Speaking to the Burnley Express, his son, Jonathan, said: "My dad remains in the high dependency unit and it's a long road, but he's making slow progress.
"He woke up in the middle of the night, missed a step and fell down the stairs and suffered broken bones and injuries to his skull. It's difficult for the family as dad's in Preston, which is an hour away from us, but my mother Rita is with him. I, my brothers Stephen and Darren, and the rest of the family are visiting him regularly.
"He is on an upward recovery and we are thankful for everyone’s love and best wishes we have received. It's been quite emotional to read the messages and see how well my dad is thought of. I will be visiting him this afternoon and passing the kind messages onto him."
Since news of his injuries broke, hundreds of fans have taken to Social Media to leave moving messages of support.
One wrote: "I hope Willie has a speedy recovery. A true Claret great." While another said: "A lovely gentleman. Get well soon. Remember watching him play for Burnley."
A Burnley FC spokesman said: "The thoughts of all at Burnley Football Club are with Clarets legend Willie Irvine, following a fall that has left him seriously ill in hospital. We pray for his speedy recovery."
Mr Irvine, a Northern Ireland international player, scored 78 goals for the Clarets and eight for his country in 23 appearances.
In 1965/66 he scored 29 goals and was the leading scorer in the old First Division
After leaving Turf Moor he also played for Preston North End, Brighton and Hove Albion, and Halifax Town ending his career at Great Harwood before hanging up his boots aged 29 in 1974.
Best wishes have also been sent by Preston North End FC. A spokesman said: "The thoughts of everyone at Preston North End are with Willie Irvine and his family, with the former PNE forward seriously ill in hospital."