Italian international Simone joined the Warriors from Benetton Treviso in 2015 and has made 29 appearances for the club at open-side flanker. The 28-year-old was voted the club’s 2015/16 Player of the Season.
Canada international prop Djustice joined the club in March 2016 and the 22-year-old has made four appearances.
Glasgow Warriors head coach Gregor Townsend said: “Simone has been a very popular figure at the club over the last couple of years and always puts in total commitment every time he plays.
“He is still a key player for us as we enter a period of important games. I’d like to thank him, as well as Djustice for all their efforts as Warriors."