The piano-sized spacecraft is the fastest ever launched, and that increases the potential for problems as it enters the crowded environment around Pluto, the U.S. space agency said.
"Because our spacecraft is traveling so fast -- more than 30,000 miles per hour -- a collision with a single pebble, or even a millimeter-sized grain, could cripple or destroy New Horizons," team member Hal Weaver of Johns Hopkins University said in a statement.
"We need to steer clear of any debris zones around Pluto."
Astronomers have been discovering more moons around Pluto. The first and largest, Charon, in spotted in1976; the fifth, tiny P5, was discovered just this summer by the Hubble Space Telescope, the Los Angeles Times reported.
The New Horizons team says it may have to think about steering the spacecraft on a "bailout trajectory" that would take it farther away from Pluto than originally intended, Southwest Research Institute planetary scientist Leslie Young said.
The mission would still be able to accomplish its main objectives, she said.
The team may not be able to determine whether they need to alter New Horizons' course until just days before reaching Pluto, team member Alan Stern said, calling the situation "a bit of a cliffhanger."