According to John Clayton of ESPN, the Lions were allocated $4,815,910 for the Rookie Pool. The Rookie pool is a mechanism within the Collective Bargaining Agreement designed to limit salaries paid to rookies. Unfortunately, it is designed poorly and consequently doesn't work effectively.
The easiest way to understand the Rookie pool is to understand that it's a "Salary Cap within a Salary Cap". The Lions have a total of $116,729,000 of salary cap space and within that $116,729,000, they are allowed to use a maximum of $4,815,910 of salary cap space to sign current year drafted players and undrafted free agents.
Typically, the Lions and all other NFL teams, sign their lower round draft picks first and sign players in reverse order from when they were drafted. The rationale for signing the players in this order is because there is more flexibility in how you can allocate payments to a first round selection as opposed to a 7th round selection. A seventh round selection will get somewhere under $40,000 guaranteed money where our first round draft pick will get somewhere in the neighborhood of $8M in guaranteed money. It's a lot easier for a team to manipulate the salary cap with an $8M guaranteed contract than it is with a $40,000 guaranteed contract.
Look for the lower round draft picks to start signing in late June or early July, Jordon Dizon to sign a week before training camp and Gosder Cherilus to sign a day before or the day of training camp.
My initial guess is that the Lions will not use all of the allotted rookie pool cap money. They'll still use all of their salary cap money, but instead of using it on rookies, they'll use it on veterans. The Lions are already tight against the cap and if they were to use all their rookie pool allotment, they'd have to cut some veterans or restructure some contracts to free up the necessary cap space to use $4.8M.
The Lions are currently about $450,000 under the salary cap and will get an additional $4M of cap space on June 1st when Kalimba Edwards (designated as a June 1 release) officially comes off the books. Typically, the Lions enter the regular season with about $2M of cap space, this will allow them to sign additional players when injuries occur and to potentially negotiate long-term contracts with players with expiring contracts. Expect the Lions to renegotiate a player contract or two and/or extend a player or two. Candidates that have contracts that could allow the Lions to free up some cap space through an extension or a contract renegotiation are Cory Redding, Roy Williams, Jason Hanson and Dominic Raiola.
Chris Patrick - Patrick was a tryout player at the Lions rookie mini-camp. He signed a one-year contract with the Lions for the league minimum and likely got a signing bonus of a couple thousand dollars. His current year salary cap cost is less than $300,000 and would not effect the Lions current salary cap status.