Messi had to be substituted midway through the first half of his side's 4-2 win at home to Sevilla after providing an assist and scoring a goal, before falling badly on his arm, reports Xinhua news agency.
He had already scored, making it 2-0 with a crisp left-footed finish, to add to a stunning opener from Philippe Coutinho.
As reported by La Gazzetta dello Sport, Radja Nainggolan, Marcelo Brozovic and Ivan Perisic all picked up injuries at the weekend, and coupled with the fact that Roberto Gagliardini isn't eligible to play in the Champions League, it could leave the Italian tactician severely short of options in midfield.
"We have the idea to solve the problems we have inside the dressing room, not outside, and we will keep things that way", said Valverde.
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"He's a big miss and it means we can go head to head [with Leo gone] because we have the qualities needed to take them on". "But it does not have to affect us".
He was replaced in the Sevilla game by French worldwide Ousmane Dembele, and he is set to start in place of Messi this weekend. Borja scored a goal in each half in Espanyol's 2-0 win away to Huesca, whose new coach Francisco debuted with a defeat after replacing Leo Franco during the worldwide break.
However, since Messi's debut in December 2004, on the rare European nights where he has not been included, that figure leaps up to 77 per cent with 17 wins in 22 games and only three defeats.
"It is not easy to change the attitude of a team just because of the absence of one player", he said.
It would be a surprise if Dembele was not at least given the chance at Camp Nou against Inter, who are level on points with Barca in Group B, having also beaten PSV Eindhoven and Tottenham.
"But Barcelona remain a team that do not chase the ball, who know where they want to pass and have the quality to find solutions for every opponent". "It is a pity", said Mauro Icardi.