The Scarlets are currently unbeaten in their pool after wins over Castres and Northampton but they will now face former champions Munster in back-to-back games - starting on Sunday at Parc y Scarlets.
And former Ireland flanker Easterby, who made more than 200 appearances for the Scarlets, claims the two clashes will shape the region's hopes
He told the club's official site: "It doesn't get any bigger than this weekend for Scarlets Rugby and the squad we've built up now - the next two weeks are going to be huge.
"We are only two games into Europe and you can't win it at this stage but games three and four are crucial and you can put yourselves out of contention very quickly.
"Winning at the weekend at home is vital to us, if we do that and then we can go to Munster and put the pressure back on them.
"We've put ourselves in a great position and the results of these next two fixtures will have a big bearing on the outcome to the group."
The Scarlets will go into the game full of confidence having lost just one in their past nine encounters and toppled Northampton away in their last Heineken Cup outing.
However Easterby insists the players remain fully focused on the job in hand.
He added: "It is about the here and now for us over the next two weeks and it can change very quickly so we're not looking ahead much or getting carried away.
"It's a tough group, but we've invested in this team over the past couple of seasons and it's starting to develop nicely and we have some depth now.
"We know on paper we have the team and players to compete with any side in the competition and if we get to knock-out rugby we know we're good at that - but consistency, belief and peaking at the right times in the group stages are important right now."
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