B737-300 CREW WAS CLRED FOR THE VISUAL BEHIND AN ACR B757. THE APCH CTLR DID NOT MENTION FURTHER INSTRUCTIONS AFTER AN RNAV INTXN.

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PASSING UTARE INTXN ON LYNSY 2 RNAV ARR INTO LAS; APCH CTL CLRED US FOR VISUAL APCH TO RWY 25L BEHIND ACR Y; B757. DISCONTINUED RNAV PROCS AND STARTED TURN OFF ARR IN ORDER TO FOLLOW B757. NOT LONG AFTER THAT; APCH CTL ASKED US IF WE ARE PROCEEDING DIRECT TO DUSJO INTXN (DEPICTED FIX ON ARR; AFTER UTARE). I RESPONDED IN THE NEGATIVE AND CTLR INFORMED US THAT HE HAD CLRED US FOR VISUAL APCH AFTER PASSING DUSJO. CTLR CANCELED OUR CLRNC FOR VISUAL APCH AND CLRED US BACK DIRECT DUSJO. FO CORRECTED BACK TO DUSJO (REENGAGED RNAV). WE WERE SUBSEQUENTLY CLRED FOR VISUAL TO FOLLOW COMPANY B737 JOINING FINAL FROM L BASE; APCHING FINAL APCH COURSE FROM OUR 8 O'CLOCK POS. COMPANY WAS AT LEAST 5-7 MI AWAY AND BELOW OUR ALT (DSNDING OUT OF 8500 FT). NO TFC CONFLICT WAS EVIDENT AND THE CTLR DID NOT INDICATE THAT ANY PROBS AND/OR CONFLICTS HAD OCCURRED. THERE WAS AN OBVIOUS MISUNDERSTANDING/BREAK DOWN IN COMS. NEITHER I; NOR THE FO; RECALL THE CTLR CLRING US FOR THE VISUAL AFTER PASSING DUSJO. WE BOTH INTERPRETED THE CLRNC TO MEAN WE WERE AUTH FOR THE VISUAL BEHIND THE B757; FROM OUR PRESENT POS ON THE ARR. HOWEVER; I DO RECALL THE CTLR MENTIONING THAT COMPANY WOULD BE SEQUENCED BTWN US AND ACR Y ON THE VISUAL APCH. PREVENTION: LISTEN UP; AND IF THERE IS ANY DOUBT; VERIFY!