This means that next Saturday's El Clasico will be one of the first in recent memory to not involve either Messi or Cristiano Ronaldo.
Lionel Messi had Barcelona hearts in mouths at the Camp Nou when he went down writhing in agony after falling badly on his right arm - he was substituted but had been generous enough to win the game for his team before he left. "He will be out for approximately three weeks", the club said on fcbarcelona.com.
This was bad news, but the night had begun in a much more positive fashion. A attractive curling strike from Philippe Coutinho in the second minute was followed by a perfectly measured pass into the corner of the net from Barça's talismanic Argentine. He then got on the scoresheet himself - his seventh LaLiga strike of 2018/19 - in the 12th minute to put Barcelona in control. Trying to cushion his landing, Messi's right elbow bent badly.
"Tests carried out on the first team player Leo Messi have confirmed that he has a fracture of the radial bone in his right arm".
Shortly after leaving the pitch, the player got into a private vehicle and headed straight to the club's medical centre for further tests.
He's the team's leading scorer with seven goals in the league after nine matches.
Lionel Messi, however, featured in both those games.
He will then be ruled out of the first El Clasico of the season when Real Madrid pay a visit next Sunday.
However, Rakitic restored Barca's three-goal advantage with a superb volley that sailed into the bottom corner.
Fast forward to the present and Real Madrid are now in a five-game winless run.
The hosts picked up from where they left off in the first half, and managed to bag a third goal in the 63rd minute when Luis Suarez converted a penalty that he won.