Spartak are bottom of Group G, pointless after two 3-2 defeats in their opening two games.
A late Lionel Messi strike put paid to their efforts in Barcelona but they were then shocked by Celtic who claimed their first away win in the Champions League courtesy of a 90th-minute winner by Giorgos Samaras.
As a result the games against Benfica, who themselves have just one point, are key to both teams.
Midfielder Jose Jurado is on loan at Spartak from German side Schalke and he acknowledges the double-header is set to be a defining moment in Spartak's campaign.
He told the club's official website: "Of course! Two battles with Benfica are crucial to the league position.
"We have to give everything 100 per cent, try to beat the Portuguese, and then Celtic at their place in order to get through to the next round of the Champions League."
Of Spartak's opponents, Jurado added: "They are a strong team with a good selection of players.
"Almost every year they participate in the Champions League and are difficult to play against."
Spartak coach Unai Emery echoed Jurado's sentiments, telling reporters: "Tuesday and in Lisbon are decisive games. We failed at home to Celtic and we can not fail again.
"We must show that we have improved."
Of Benfica, he said: "It's a team accustomed to winning.
"But the Champions League is an important test and all have to be committed. We have great respect for Benfica."
Benfica midfielder Andre Gomes has found himself making the progression from the B team and may well face the Russians tomorrow.
The club are currently second behind Porto in the Portuguese Liga on the most narrow goal difference.
However, they also need to at least avoid defeat tomorrow night, with their sole point so far coming in a 0-0 draw with Celtic.
They were beaten 2-0 by Barcelona last time out and Gomes has no illusions about the importance of tomorrow night's match
In quotes reported on record.xl.pt, Gomes said: "We want the three points.
"We are facing a great team, but we want to get the win."
Of his own elevation from the B team, he added: "We are proud to represent club like Benfica.
"All players representing Benfica have a great responsibility to win over the fans and contribute to the good of the club."