The Argentinian soccer star appeared to be clutching his right elbow when he exited the game.
'He will be out for approximately three weeks'.
"It makes a big difference to have or not to have him but we have enough cover so as not to worry about whether he is there or not".
In Messi's absence it will be important for Ter Stegen to ensure stability at the back if things don't go too well in the forward areas for Barca.
Inter Milan's Spanish account sent a classy message to Lionel Messi after he was ruled out of the Champions League clash at the Nou Camp on Wednesday.
"#Messi has a fracture in the radius of the right arm".
Messi left Barca's La Liga match against Sevilla in the 26th minute on Saturday.
"I know who Leo is", Maradona, who is coaching Mexican side Dorados de Sinaloa, said after his team's 3-2 win at Mineros de Zacatecas at the weekend.
With Messi off the field, Luis Suárez added Barcelona's third through a 63rd-minute penalty, before Pablo Sarabia pulled one back for the visitors.
He stopped two certain goals of Sevilla with double saves from point blank ranges and put a few of Andre Silva's headed opportunities out of the Barcelona net.
Meanwhile, Real Madrid suffered their fourth loss in five games and set an unwanted record with a 2-1 defeat by Levante at the Bernabeu.
"We drifted out of the game after a good start to the second half and, instead of making it 2-0, we let them make it 1-1", Allegri said.
Real Madrid was four points behind Barcelona, in fifth place.