Argentina forward Messi damaged knee ligaments in Saturday's La Liga win over Las Palmas and will be out for around eight weeks, leaving Brazil forward Neymar and Uruguay striker Luis Suarez to take on much of the goal-scoring responsibility.
Messi's absence could hand youngsters Munir el Haddadi and Sandro Ramirez a chance to impress.
"Of course it affects us a lot," Rakitic told a news conference previewing Leverkusen's visit to the Nou Camp when asked about Messi's injury.
"Not having the world's best player hurts but it also motivates us," added the Croatia international.
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"A new door is opening. We have 100 percent faith in ourselves and together we can do it."
The Leverkusen players may be breathing a private sigh of relief that four-times World Player of the Year Messi is unable to play on Tuesday.
He became the first player to score five goals in a Champions League match when Barca hammered the Bundesliga side 7-1 in the 2012 round of 16.
Leverkusen's Mexico striker Javier Hernandez said he would never be pleased about an injury to a fellow professional and insisted his new club had a good chance of getting at least a point out of their trip to the Catalan capital.
Barca drew their opening Group E game at AS Roma 1-1, while Leverkusen hammered visiting BATE Borisov 4-1 and are top.
"It's always a bad thing when a player gets injured," Hernandez told Spanish sports daily Marca on Monday.
"Seeing a human being suffer is never pleasant," added the former Manchester United and Real Madrid player. "Health is the most important thing in life."
Barca are unbeaten at home in the Champions League since losing 3-0 to Bayern Munich in May 2013, their only defeat in their last 33 matches at the Nou Camp in Europe's elite club competition.
(Writing by Iain Rogers, editing by Martyn Herman)
