England goalkeeper Fraser Forster does not know if he will still be at Celtic when they next play in Europe.
Norwich captain Sebastien Bassong has signed a new two-and-a-half-year contract.
The 22-year-old, a former France Under-21 international, was given the all clear to switch to the French club following an approach before the transfer deadline.
Gueye, who moved to Goodison Park from Strasbourg in June 2010, has made just six appearances for the Toffees this season.
Brest are currently only four points above the Ligue 1 relegation zone.