Kieran Richardson, Charles N'Zogbia and Philippe Senderos are all heading for the Villa exit door – but Lendro Bacuna has signed a new long-term deal.
Sunderland are rumoured to be interesting in re-signing Richardson as they bid to shore up a defence that has leaked seven goals in the opening two games of the season.
And with Villa currently having 29 players in their 25-man senior squad, Sherwood needs to trim some from the payroll before September 1.
"There are still some players here who know they can find other clubs," the Villa boss said. "But I think the balance of the squad is getting a lot better."
Sherwood has brought in nine new players this summer, spending almost £50m, although that was tempered by the big-money sales of Christian Benteke and Fabian Delph.
Meanwhile, Westwood has been told he can be the new Michael Carrick.
"I will be very surprised if Ashley doesn't play for England this season," Sherwood said. "He's as good as that.
"He's probably the single-most consistent player I have had at the club since I arrived.
"He's very much in the Michael Carrick mould."
Meanwhile, Leandro Bacuna has signed a new five-year deal at Villa.
The 23-year-old, a £3million signing from FC Groningen in 2013, has made 66 appearances for the club.
Bacuna said: "I am absolutely thrilled to sign a new contract and continue my time at Aston Villa.
"I love it here and am really excited about my future in claret and blue under the manager.
"I feel I can really develop here and show my worth to the team and I think there are bright times ahead for us all."