not exactly the case for players who are under contract in another league. theres a process by which the player has to pay the buyout of his existing overseas contract, and then he gives the nba team formal notice that he is available to sign an nba contract. at that point, the team has a limited period of time to tender him a second round minimum contract.
if cissoko is still under contract with baskonia, he isnt currently eligible for an nba contract. the buyout has to happen first. often times, this is negotiated, and the team gets involved and pays some money directly toward the buyout, and usually will factor in the rest of the required buyout money into the player's contract
the spurs can tell cissoko that they have no obligation to offer him a contract until he gets out of the baskonia deal. if the spurs want him stashed, they can simply say they are unwilling to participate in his buyout. that could turn into a scola situation. or maybe cissoko agrees that he's better off staying on his deal with baskonia (and potentially being rented to the gleague again) rather than forcing his way onto a back end nba roster spot and not getting playing time anyway
and no, cissoko certainly hasnt "earned a rotation spot" lol. he's played ok enough defensively against summer league compe ion, but thats a far cry from real nba games. and his lack of scoring ability has been an eye sore. he's definitely not rotation ready. and thats to be expected. he was a mid 2nd round pick. thats usually not a recipe for year 1 real rotation minutes