A Barcelona statement read: "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".
'He will be out for approximately three weeks'.
"It's a significant loss, given who we're talking about", Barcelona manager Ernesto Valverde said in a postmatch conference.
Lionel Messi picked up a potentially-serious injury to his right arm in Barcelona's 4-2 win over Sevilla at Camp Nou on Saturday night.
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The hosts got off to a fast start at Camp Nou, with Phillipe Coutinho scoring in the second minute.
Then came the innocuous clash with Franco Vazquez and a odd five minutes as Messi seemed to be far more concerned about his injury than the Barcelona bench.
Local media immediately questioned whether Madrid should fire Lopetegui before the clasico next weekend at Barcelona or give him a chance to try to save his job against the rival. Sevilla coach Pablo Machin said afterwards.
It appeared that the South American would return having been strapped up, but the decision was made to replace the 31-year-old, with Ousmane Dembele entering the field. Suarez buried the penalty.
Then, in typical Messi fashion, he raced towards Sevilla's backline before dipping onto his left foot and beautifully finding the bottom corner in the 12th-minute to make it 2-0.
Sarabia's 79th-minute reply took a vital deflection off former Sevilla defender Clement Lenglet to ruin Ter Stegen's clean sheet, the Germany goalkeeper then making a second double save.