Speculation Caterham has decided to install an all-new race lineup for 2014 became certain on Tuesday.
On Monday, team boss Cyril Abiteboul told French television that Charles Pic will not be driving for the team this year.
It further solidifies rumours Caterham will shortly confirm returning Japanese driver Kamui Kobayashi alongside Swedish rookie Marcus Ericsson for 2014.
Sauber said Dutchman van der Garde, 27, will this year take part in "some Friday sessions and several tests".
"He has four years experience in GP2 and he drove one year in formula one," team boss Monisha Kaltenborn said. "These are good credentials to work successfully with our team."
Van der Garde, who is sponsored by McGregor and married to its chief Marcel Boekhoorn's daughter, said in the media statement that he wants to prove this year "that I deserve a race seat with the Sauber team in 2015".