Borini will join Serie A side AC Milan on a permanent deal after spending the 2017/18 season on loan in Italy, making 44 appearances and scoring 5 goals.
Dutch international Lens will follow suit, joining Turkish side Besiktas where he spent last season on loan.
However, fellow loan stars Wahbi Khazri, Papy Dilibodji and Didier Ndong, who spent spells at Rennes, Dijon and Watford respectively, have all been retained.
Among those released from the first team were defenders Billy Jones and Marc Wilson and winger Kazenga LuaLua, who will all depart the club upon the expiration of their contracts on June 30.
June 7, 2018