Just hours after Rodrigo Palacio brought up his 18th goal of the season with a brace at Sampdoria, the Argentinian winger was ruled out for up to a month with a thigh injury suffered in training.
That left Inter with just two senior strikers - Antonio Cassano and Tommaso Rocchi - but Pereira hopes his midfield colleagues will step up to the plate for the season run-in.
He told inter.it: "It is terrible news but now we have to think about the game on Sunday and those players who can still do their jobs, even if it won't be easy.
"We have to concentrate and think exclusively about beating Atalanta.
"Now Cassano and Rocchi are the only available strikers and we have to consider the possibility that other attack-minded players will be asked to get forward."
Inter were seven points shy of city rivals AC Milan going into the weekend, with daunting matches against Lazio, Napoli and Udinese still to come and threatening their concerted bid to reach third place.
"Everybody wants it, we believe we can do it, and there are still lots of matches left," the former Porto winger added.
"But first we have to do well against Atalanta on Sunday. Every match is difficult. We still believe in third place and we know that our fans believe in it too."
Midfielder Walter Gargano serves a one-match ban with Gaby Mudingayi, Luca Castellazzi and Yuto Nagatomo still missing through injury.
Diego Milito, Cristian Chivu and Dejan Stankovic have all returned to light training but will not feature at San Siro.
Atalanta boss Stefano Colantuono, meanwhile, is optimistic striker Maxi Moralez will be fit in time to feature after he limped out of last week's goalless draw with Sampdoria.
"He went off injured but I hope it's nothing serious," Colantuono said. "Let's hope that the warmer weather helps him."
On-loan Inter striker Marko Livaja does return to contention after serving an internal suspension for undisclosed disciplinary reasons, while defender Stefano Lucchini and goalkeeper Andrea Consigli serve one-match bans.
Referring to Livaja, Colantuono added: "I've nothing to say except that we will be back with us. There was an incident and we have rules, which he knows must be respected."