Max Chilton fears a revival from Sauber could cost Marussia their ninth place in the Constructors' Championship.
As F1 enjoys its summer break, Marussia are in the unexpected position of leading Sauber in the teams' Championship thanks to their two points compared to Sauber's zero.
The Hinwill team has had a wretched start to this season as their best finish has been two P11s.
In contrast Marussia are in the midst of their best campaign ever thanks to Jules Bianchi's ninth-place finish at the Monaco GP.
But with Sauber showing a better form in the last race, Chilton admits he is wary of the threat they pose.
"We'd love to hold them off," the 23-year-old Briton told Press Association.
"But to do that we need to be finishing in front of them, and at the moment we're not doing that, so we're hoping in a race when points do become available, they're not in front of us.
"We're giving it our best shot, but without constant updates on the car it's hard to keep knocking on their door.
"Some races we're close, some we're not as close.
"Thankfully for us they're not closing the door on the teams in front of them.
"It's not like they're looking at points every race and they're just missing out. They're not there at the moment.
"Because they're not in a position where they can feel comfortable scoring points, it means we're not right on the edge of our seats.
"They need a bit of luck like we had."
As for Marussia's traditional rivals Caterham, Chilton feels their recent takeover could cost them possibility of pipping Marussia.
"They've gone through a lot of changes. I've heard stuff about people going and different people changing roles.
"Like any sport, if you change people around it takes time for them to learn their new positions and communicate properly.
"It takes a bit of time for a team to settle down, so for us that's helping."