Lurking amid the well-earned good feelings from the Union’s tie in Columbus on Sunday night was a sign of potential trouble on the horizon.

You might have noticed that Union manager Jim Curtin made just one substitution. He was fortunate that he didn’t have to make more, and he heaped credit on the fitness staff for having Jamiro Monteiro and other stalwarts ready to play every minute again.

But Curtin knew the truth, and he didn’t hide from it. While he carried a full bench on paper, the Union’s high-ceiling, homegrown rookie crop isn’t ready for the big time yet.

“Our bench right now is very defensive, and it’s very thin,” he said. “It’s no secret that we miss Ilsinho and Cory [Burke].”

» READ MORE: Union start regular season with hard-fought scoreless tie at MLS champ Columbus

There’s no doubt about that, and their returns from injury — potentially as soon as this week — will be a big help. The same goes for Jack de Vries, though his timetable on returning from a concussion won’t be the same.

Once they’re all back healthy, Curtin will be able to move Anthony Fontana back to midfield and platoon him, Monteiro, Leon Flach and Alejandro Bedoya through a stretch of three straight weeks with weekend and midweek games.

That still won’t give the Union the depth they need in central midfield, though. The drop-off from the starters to 17-year-olds Quinn Sullivan, Jack McGlynn and Paxten Aaronson is still too big to throw them to the lions in a road game against an elite opponent.

Which is why Curtin didn’t do it Sunday night.

“We’re going to give these guys opportunities, but it has to be an opportunity that number one, they earned, and number two, that makes sense,” he said. “To throw a kid into that game can also be counter-productive to their development. You want to set them up for success. You throw them into the last 10 minutes of that game, and I just would say nothing good can come of it.”

Especially when you’re trying to lock down a well-earned tie, as opposed to holding a lead. The latter scenario was the case in the Champions League home game against Saprissa, when Sullivan played the last 14 minutes once the Union had the result wrapped up.

Now, what if the Union were in a situation to go for a win, but unable to break through an opponent’s defense? That has happened plenty often in the past.

Having Ilsinho and Burke or de Vries on the bench would help, for sure. But neither of them is a great fit for a central midfield role if that’s what’s needed.

» READ MORE: Jamiro Monteiro again shows Union fans — and the front office — why he’s so important

McGlynn, Sullivan, and especially Aaronson all have the potential to be that player. They will be in time, perhaps even later this year. But they aren’t yet.

“We’re a little thin right there, you’re definitely right on that, especially with the attacking punch off the bench,” Curtin said. “But I think we’ll get stronger here in the coming weeks.”

The point has been made enough times here that the best way to do that would be through a new signing. At this point, it will probably have to wait until the summer transfer window opens.

Until then, hope that the players returning from injury will help cover the gap, and let Monteiro, Bedoya, Flach and Fontana get some deserved rest along the way.

Key performances Sunday

Andre Blake was rightly hailed for his six saves, but the most impressive individual performance came further up the field. Bedoya stepped up big in the attack, with three shots, two chances created, five aerial duels won and 27-of-32 passing.

Those contributions were especially important with Fontana held to just 14 touches — the same number Santos recorded after replacing Fontana in the 61st minute.

Flach was also very good: 64 touches, one chance created, one shot, 28-of-37 passing, six tackles and nine recoveries.