The Everton defender had to be given oxygen before being carried off after he was brought down by Neil Taylor, who was shown a red card for his horrific approach.
Ireland slip to second in the Group D standings, level on points with Serbia at the top but behind on goal difference.
FAI chief executive John Delaney also sent his best wishes to a player who has become a mainstay in the Republic team.
Ireland now top Group D, having accrued 10 points from four matches, while Wales are third, four points adrift of O'Neill's side after winning just one fixture so far.
"He is a really strong character and he has a great family around him and we, his extended family at Everton, will be here for him to help him get through this over the coming days, weeks and months".
Joe Allen, Gareth Bale and Ashley Williams were all victim to late elbows to the face but Rizzoli remained ignorant.
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James McClean featured in the match for the Republic of Ireland.
The incident proved to be a turning point in the game with 10-man Wales deciding to try and soak up Irish pressure who, devoid of the creativity the likes of Wes Hoolahan or Robbie Brady provide, couldn't break them down. "And you wouldn't call Wales out of it either".
Wales will be disappointed in the way they handled the clash having played into the physical game plan of the boys in green. Both are four points clear of Wales.
The remainder of the schedule that awaits O'Neill's side looks easier on paper than what has gone before, with group leaders Serbia coming to Dublin as well as Austria and Moldova with away trips to Georgia and Wales.
While some players come away from their clubs with moans ringing in their ears from club managers who don't care about worldwide football, it's different at West Ham under Slaven Bilic, who of course managed Croatia in the past, Randolph admitting that Ireland taking points off Serbia in Belgrade gave Bilic cause to smile.