At the moment, the Reds have 44 players on the 40-man roster (four of which are on the 60-day DL). Therefore, at least four of the existing players will need to be cut/non-tendered following the season. If you'd like to protect someone from the 40-man roster, you'd have to cut/non-tender an additional person.
Here are the players under contract for 2010:
Bronson Arroyo
Homer Bailey
Francisco Cordero
Johnny Cueto
Carlos Fisher
Aaron Harang
Daniel Ray Herrera
Sam LeCure
Mike Lincoln
Matt Maloney
Ramon Ramirez
Arthur Rhodes
Daryl Thompson
Pedro Viola
Edinson Volquez
Wilkin Castillo
Ryan Hanigan
Craig Tatum
Yonder Alonso
Kevin Barker
Juan Francisco
Paul Janish
Brandon Phillips
Danny Richar
Scott Rolen
Adam Rosales
Drew Sutton
Joey Votto
Wladimir Balentien
Jay Bruce
Chris Dickerson
Darnell McDonald
Drew Stubbs
Willy Taveras
Would need to be offered arbitration/contract extension:
Bill Bray
Jared Burton
Justin Lehr
Nick Masset
Micah Owings
Kip Wells
Ramon Hernandez
Corky Miller
Jonny Gomes
Laynce Nix
Players to consider protecting:
SP
Luis Montano
Oscar Castro
Leo Astorga
Jordan Smith
Luis Machuca
James Avery
Dallas Buck
Ben Jukich
Travis Wood
Tom Cochran
Alex Smit
Travis Webb
RP
Enerio Del Rosario
Sean Watson
Ruben Medina
Logan Ondrusek
Federico Baez
Greg Atencio
Jeff Kennard
Derrik Lutz
Ben Davis
Lee Tabor
Phil Valiquette
C
Chris Denove
INF
Wes Bankston
Logan Parker
Kris Negron
Miguel Rojas
Chris Valaika
OF
Chris Heisey
Sean Henry
Danny Dorn
Shaun Cumberland
Lew Ford