Force India believes it must switch its focus in the constructors' championship to defending from Williams rather than attacking Sauber, following its low score in the Abu Dhabi Grand Prix.
Williams took 12 points out of seventh-placed Force India's advantage when it got both cars home in the points in Abu Dhabi, while Sauber pulled further away thanks to Kamui Kobayashi's sixth position.
Force India had to settle for ninth with Paul di Resta after the Scot and team-mate Nico Hulkenberg collided at the first corner.
Deputy team principal Bob Fernley told AUTOSPORT: "Williams are now 22 points behind us and Sauber are 29 points ahead of us. It becomes a very difficult situation.
"It's battle on. But realistically, if we're sensible about it, I think the chances of us catching Sauber are a bit limited.
"Can Williams catch us? Every possibility I suppose. We've got to make sure we do our job in the last two races."
Di Resta was running fifth in Abu Dhabi having stopped for tyres under the lap nine safety car and then jumped up the order as others pitted.
Fernley admitted that it was tempting to consider leaving di Resta out until the finish, but that the team ultimately felt it wiser to play safe and stop again during the second safety car period.
"The data and everything was telling us 'no' [the tyres won't last]," Fernley said. "But you always like to have track position.
"What we had to gamble on really is that if we came in and did that tyre stop with the safety car, we were guaranteed points.
"Had we stayed out, we gambled on big points or nothing. Our worry was that it would be nothing.
"We probably took the safer route, and it proved a reasonably good decision, I think."
Asked how marginal the decision was, Fernley replied: "The feeling was that we couldn't do it. But you should never say never.
"Sometimes you can do things that you don't think are achievable. We've done that before in places like Bahrain, where it didn't look like it could be done either.
"But I think the safety choice was to guarantee a points finish, which is what we did."