Paul McGrath, Ian Wright and Andy Cole were among the former footballers to welcome Roy Keane to Instagram.
The Manchester United legend shocked many by opening an account on the social media platform on Friday.
He has already reached almost one million followers, with his only post to date being liked more than 600,000 times.
The photo shows Keane smiling as he poses with his dog. He commented on it: "A man’s best friend."
Replying to the post, fellow Republic of Ireland great Paul McGrath said: "Welcome to the madness pal."
Manchester United commented: "This is going to be good."
Ian Wright posted four love heart emojis, while Andy Cole posted: "Love it skip."
Sky Sports presenter David Jones added: "Welcome ... this could be interesting."
It comes a week after Keane was left disgusted by a viral video of his likeness from the FIFA video game.
Co-pundit Richards showed Keane a video of his digital self busting out some celebratory moves in the popular football title - and had to dub his own audio over the clip to mute the X-rated reaction.
Graeme Souness was even left giggling at the hilarious clip from Sky's Super Sunday coverage.
