The centre-half goes straight into Jack Lester’s squad this afternoon after signing a two-and-a-half-year deal on Thursday.
Whitmore left Burnley to join the Spireites and he picked a good week to move over, with the squad still enjoying the lift from a victory over the league leaders ahead of another crucial game.
Yeovil are the side directly above Chesterfield in the League Two table, with a four-point cushion.
“It’s a huge game but we’re in a great position to go down there and pick up some points, whether it be one or three,” said Whitmore.
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“Especially after that result, it does wonders for the lads’ confidence and I really believe we can go down there and get something.
“Everyone is positive, it was a massive confidence booster beating Luton.
“It really does feel like it’s time to kick on now.”