Lenac joined Warriors on a training contract at the start of the year and made his debut in the final match of the 2020/21 Guinness PRO14 season, coming off the bench in a 46-25 win over Benetton at Scotstoun.
Former Scotland U20 winger Nairn left Warriors at the end of last season after four years at Scotstoun.
According to French media, Leone Nakarawa is close to joining up with Toulon. The former Glasgow lock was supposed to join Ulster at the end of last season but the move fell through due to a medical issue.
Reports from France also claim Huw Jones' move to Bayonne has fallen through after the club's relegation.