LOS ANGELES -- Wednesday's move was merely a precursor, a warm-up -- a contractual formality setting up a complex series of negotiations.

The Los Angeles Rams exercised their fifth-year option on Aaron Donald's rookie contract, one that will pay the game's best interior defender a little less than $6.9 million in 2018.

But what the Rams really want to do is lock Donald up long-term, which would probably require making him the game's highest-paid defensive player. Picking up Donald's option buys them some time in that pursuit. But ideally, the Rams would get an extension done by the end of this summer, guaranteeing Donald future dollars in exchange for what they hope would be a slight discount.

One problem: The Rams have almost an entire starting defense eligible for free agency in less than a year.

The list is daunting. It includes their primary cornerback (Trumaine Johnson), their potential No. 2 cornerback (E.J. Gaines), last year's leading tackler (inside linebacker Alec Ogletree), the starting strong safety (Maurice Alexander), the starting strongside linebacker (Connor Barwin), the starting free safety and slot corner (Lamarcus Joyner), a key backup safety (Cody Davis), and three defensive linemen critical to their depth at the position (Dominique Easley, Ethan Westbrooks and Tyrunn Walker).

The Rams have roughly $112 million in salary-cap space committed for 2018 and roughly $79 million committed for 2019, which is reasonable. But the team must give significant raises to several of its key defensive players, because (a) they're good and (b) there's not much depth beyond them. Over the last two offseasons, the Rams have lost two starting safeties, Rodney McLeod and T.J. McDonald, and their best cornerback, Janoris Jenkins. They also haven't drafted a defensive player higher than the sixth round over the last two years, though that may change later this month.

Donald's situation looms over everybody else's simply because the Rams must allocate a significant amount of cap space for him several years down the road. But timing makes the other cases a bit more urgent.

Below is a list of five key looming free agents who could warrant an extension before the start of the coming season.

Johnson: The Rams had been shopping Johnson, but his price (nearly $17 million on a second consecutive franchise tag) and the presence of Richard Sherman on the trading block greatly limited his market. The Rams failed to lock Johnson up last offseason, and general manager Les Snead said they waited on extension talks this offseason in order to first see if he would be a fit under new defensive coordinator Wade Phillips. The two sides still have until July 15 and could restart negotiations at the end of the offseason program. Along with the obvious motivation of solidifying the position long-term, the Rams would also like to lower Johnson's 2017 cap hit. It would provide more wiggle room for the Rams to give their other looming free agents more money in 2017, which some may require as part of a contract extension.

Ogletree: He seems like the most obvious, and likely, extension candidate. Ogletree was a captain while transitioning to middle linebacker under Jeff Fisher last year, and is still considered a leader on the defense. There are several players the Rams want to take a longer look at to see if they'll be a fit under a new defensive system. With Ogletree, there isn't much doubt. They think his combination of athleticism and strength are ideal under Phillips, who gets creative with his linebackers. Asked about getting some long-term security on Monday, Ogletree said: "It’ll happen when it happens. Right now, my focus is being here for OTAs and going through the install. I’ll be here; not really worried about the contract thing."

Alexander: Pro Football Focus identified Alexander as the NFL's most improved safety last year, his grade jumping from 44.6 to 83.4 in his first full year as a starter. Alexander played free safety in 2016 but will replace McDonald as the starting strong safety in 2017. At 6-foot-1 and 220 pounds, he's a nice fit at that spot. And the Rams would like to see that take place beyond just this coming season. Their depth has eroded very quickly at safety.

Joyner: In 2015, Joyner emerged as a dynamite slot corner. In 2016, he was named a starter. In 2017, the plan is to keep him on the field for every defensive snap. Joyner will split time in the slot and at free safety, which he also played at Florida State. The Rams may want to wait and see how he takes to the position before seriously considering an extension, but they love his instincts and tenacity. His 5-foot-8, 184-pound frame is not much of an issue.

Gaines: Gaines wasn't selected until the sixth round in 2014, but he impressed as a rookie, stepping in for an injured Johnson and starting 15 games. But he missed all of 2015 with a foot injury and was limited to 10 starts in 2016. Since then, the Rams have signed Kayvon Webster, who spent the last two years playing under Phillips with the Broncos and will compete for a starting job. Gaines may need to prove he can stay healthy before being signed long-term.