The set of radial velocity measurements of the HD 160691 has been recently published by ( ) .
It reveals a linear trend that indicates a presence of the second planet in this system .
The preliminary double-Keplerian orbital fit to the observations , announced by the discovery team , describes a highly unstable , self-disrupting configuration .
Because the observational window of the HD 160691 system is narrow , the orbital parameters of the hypothetical second companion are unconstrained .
In this paper we try to find out whether a second giant planet can exist up to the distance of Jupiter and search for the dynamical constraints on its orbital parameters .
Our analysis employs a combination of fitting algorithms and simultaneous examination of the dynamical stability of the obtained orbital fits .
It reveals that if the semi-major axis of the second planet is smaller than \simeq 5.2 AU , the observations are consistent with quasi-periodic , regular motions of the system confined to the islands of various low-order mean motion resonances , e.g. , 3:1 , 7:2 , 4:1 , 5:1 , or to their vicinity .
In such cases the second planet has smaller eccentricity \simeq 0.2 - 0.5 than estimated in the previous works .
We show that the currently available Doppler data rather preclude the 2:1 mean motion resonance expected by some authors to be present in the HD 160691 system .
We also demonstrate that the MEGNO-penalty method ( MEGNO is an acronym for the Mean Exponential Growth factor of Nearby Orbits ) , developed in this paper , which is a combination of the genetic minimization algorithm and the MEGNO stability analysis , can be efficiently used for predicting stable planetary configurations when only a limited number of observations is given or the data do not provide tight constraints on the orbital elements .