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Charlie Lyon waits for the phone to ring.

Sometimes it does. Most often, it doesn't. The frustration seems unbearable. Lyon, however, keeps going.

Being a pool keeper in MLS is a tough gig.

He is there as a back-up for all 24 teams. A contracted league employee ready to down tools in an instant, the sought-after band-aid in the midst of an injury crisis.

If two keepers go down, call the pool keeper.

And even after all the sweat, tears and uncertainty subsides, the meal ticket you've been craving can disappear before the first bite.

Lyon, who's currently based in Portland, Oregon, and trains with the Timbers, is an outsider floating on the edge, enviously peeking over the wall at those more fortunate.

"I am just thankful to be involved," a smiling Lyon told Bleacher Report after another round of training, another morning of going through the motions.

Introduced over a decade ago to help smaller rosters (then numbering around 20 with just two keepers but have now increased to almost 30 with three keeper slots) impacted by injury, MLS are keen to maintain this unique role, especially for cases of extreme hardship.

It's also helpful for franchises who don't have any affiliate teams.

Portland, for example, have a side in the USL, effectively the second tier in U.S. soccer, so temporarily dropping down is possible for Lyon.

Some players, however, aren't so sure of the system's feasibility.

"I don't think it's necessary anymore," said Sporting Kansas City keeper Tim Melia, a success story who completed the journey from pool keeper to first choice with aplomb.

"There are so many options for teams these days with academy set-ups and affiliate teams.

"And that hurts to say because it was my path, and one I am proud of."

For any team suffering a keeper crisis, a quick message to MLS headquarters is all that's needed.

One moment Lyon is training in Portland, and the next he's packing his bags again.

Game time isn't guaranteed. Neither is stability. His wife is searching for work as a software developer in the Portland area but knows anything can happen.

Lyon, to his credit, composes himself commendably. Deep down, it must hurt.

The startling lack of opportunity to show what he's all about must sear the soul of a proud, professional sportsman.

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Philadelphia Union came calling in May after first-choice keeper Andre Blake and understudy Matt Freese suffered injuries.

It lasted nine days.

Great experience? Absolutely. Game time? Zero minutes.

"It was exciting," he said. "They have a great squad, but I knew it was unlikely I would play."

He's been training with the Timbers since the start of the season but hasn't suited up.

Everyone needs a chance to shine. That said, Lyon's opportunities, sadly, have been few and far between.

For the 27-year-old from Illinois, the wait continues. His dream refuses to wilt, even if stark realities smack him in the face every single day.

Portland's roster is set. Coach Gio Savarese is pleased with his keepers, so Lyon, who was drafted by Seattle in 2015 and also spent time at LAFC before his contract wasn't renewed at the end of the last campaign, plays the waiting game.

When his contract expires at the end of the season, he can't rely on Portland's hospitality for the next 12 months.

What's the lifespan of a goalkeeping nomad?

"Thoughts start to creep in," he admitted when asked what's next.

"I sent out some applications recently for college coaching jobs but didn't hear anything back."

Lyon is very open-minded—he's had offers recently from the new USL League One—if it means precious minutes on the pitch. The only substantial game time in his career has come from USL teams—Tacoma Defiance and Orange County SC.

"I think the unique structure of MLS allows this contract to exist," he continued.

"I've done it long enough now, you don't have the expectation of it (playing), apart from just training and doing everything you can to be prepared."

Yet, while Lyon plugs away, hope springs eternal.

In 2014, Melia was that guy. The 33-year-old bounced around, never losing hope. He did the hard yards, emerging from the dysfunctional chaos at Chivas USA with hope. He banged down doors elsewhere, pleading for a chance.

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At the culmination of that season, he was recruited for D.C. United's play-off push but ended up being sent home the very next day.

A four-month spell as a pool keeper in 2014, however, gave his career the springboard he'd been seeking. A seven-year pro with a paltry five MLS starts had finally found a place to call home the following season after a spell in Kansas morphed into something permanent.

The native New Yorker, undoubtedly, feels Lyon's pain.

"The biggest thing is you're not really part of the team," he told Bleacher Report over the phone after training.

"You're not part of the group, but I also think it's how you handle yourself when you are there. Because when you are a pool goalkeeper, you are on their roster. Even though you've got take it with a grain of salt."

So what would Melia, who was eyeing a job in finance as a back-up career before becoming No. 1 at Sporting KC, tell Lyon right now?

"Do everything you can in Portland to get yourself in the best possible shape," he advised.

"When an opportunity arises, make sure you're fresh and sharp, and they're going to remember you."

Melia knows, however, practicing what you preach is tough.

"It's not easy to grind," he admitted.

"But there was never a time where I felt defeated because I was getting released.

"It's not in my nature. It's the same thing as like when you're on a rough time with the team. Things will change. I always approached it like that."

While Melia's rise continues, so, too, does Lyon's push for recognition. The battle for a starting jersey wears on, and it's one he will continue to fight for with a smile and the acceptance of his role, which is equally admirable and dispiriting.

"It's a test of patience," he concludes.

"If you let that frustration start to overwhelm you, it takes away from the fact that I'm going out there every day. I could've been at home doing something different.

"But I am still in the game."

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