Luiz, 29, left Chelsea for Paris St Germain in 2014, but re-signed with the London club on transfer deadline day after a trophy-filled spell with the French champions.
Spanish left back Alonso joined Chelsea from Fiorentina last month.
"I think the new players need a bit of time to work with a new method, a new philosophy, a new idea of football and it's important to give them a bit of time," Conte told reporters.
"For this reason their chance of playing from the start is not high."
The former Italy and Juventus coach opted for a 3-5-2 lineup for his country at Euro 2016 but said he would use three defenders after Luiz's arrival.
"It can be an opportunity, a solution. It can happen in the future. This squad can play with 3-4-3, not 3-5-2 like the Italy national team or Juventus, because of the characteristics of the players," Conte added.
Chelsea, second in the standings, have won their opening three league games this season while Swansea are 14th following one win and two defeats.
(Reporting by Ian Rodricks in Bengaluru, editing by Ed Osmond)
