WILMINGTON — A week into the Union’s preseason, there’s only so much we can know about the team. But there’s one thing we know for sure: it has some significant missing pieces.

Mark McKenzie and Brenden Aaronson are out of town with the U.S. national team at its annual January training camp, as both players make their push for a spot on the Olympic qualifying team.

New midfielder José Martínez and returning star Jamiro Monteiro weren’t around this week either, as they’re waiting for their immigration paperwork to be cleared.

Even if they were all here, there would still be holes to fill. The roster still has only three centerbacks — Jack Elliott, Mark McKenzie and Aurélien Collin — and both manager Jim Curtin and sporting director Ernst Tanner have made no secret of needing to sign another one.

There are also some quiet questions about the Union’s attacking midfield depth chart. Aaronson is the only true attacking playmaker on it right now. Monteiro and Anthony Fontana can play the role, and Monteiro probably will for some stretches. But outsiders and insiders alike have a sense that the team needs a further addition — especially when it comes to shooting and scoring from long range.

That was, as has been written here many times, Marco Fabián’s greatest strength and one of Aaronson’s few weaknesses.

Aaronson knows it and has been working on it, and there’s little doubt he’ll get better at it. He’s going to miss a big chunk of March if he makes the Olympic qualifying team, though. And if the U.S. books a trip to Tokyo and Aaronson makes the team, he’ll be gone from mid-July into early August. That’s a lot of time.

So it might not be a bad idea for the Union to bring in another attacking midfielder.

“I don’t think our roster is totally finalized yet, so I still think that you’ll see a move or two,” Curtin said at Friday’s practice.

That player might not be a big-time name — probably won’t be, really, unless Tanner has a very well-kept secret up his sleeve — so everyone else is going to have to do their part.

“It’s not going to be any one guy that just plugs in,” Curtin said. “It’s going to be a little bit by committee."

In some ways, that won’t be a bad thing. Kacper Przybylko certainly would appreciate it if enough other players get goals so that opposing defenses won’t overload on him.

Curtin will learn a lot more about what he has right now when the Union head south to Clearwater, Fla., next Monday, and get outside on a real grass field. They spent this week on indoor turf at the 76ers’ Fieldhouse in Delaware, which also includes the Blue Coats’ arena.

Next week will be the first time Monteiro, Martínez and fellow newcomer Matej Oravec get to play together.

“We’ve seen them, scouted them and know what they’re about, but now getting them all together and acclimated as teammates with their teammates is still something we don’t have the final recipe for quite yet,” Curtin said.

The Union will take two trips to Clearwater, starting with an 11-day camp that will run through Feb. 6. The team will once again be based at the Joe DiMaggio Sports Complex, just down the street from the Phillies’ spring training home, and will play three scrimmages on the trip (see below for the schedule).

They’ll return to Philadelphia until Feb. 10, then fly back to Clearwater and stay through the 23rd. They’ll play four more scrimmages on that trip. Some will be open to the public, including a Feb. 19 game against FC Dallas — the team the Union open the regular season against 10 days later. Broadcast details are still to be confirmed.

Union preseason scrimmage schedule

All times listed are Eastern.

Jan. 29: vs. Atlanta United at IMG Academy, Bradenton, Fla. (11 a.m., closed)

Feb. 1: vs. Chicago Fire at Joe DiMaggio Sports Complex, Clearwater, Fla. (4 p.m., closed)

Feb. 5: vs. Montreal Impact at Joe DiMaggio Sports Complex, Clearwater, Fla. (7 p.m., closed)

Feb. 12: vs. FC Cincinnati at IMG Academy, Bradenton, Fla. (4 p.m., closed as of now but might be opened)

Feb. 15: vs. Inter Miami at Al Lang Stadium, Tampa, Fla. (4:30 p.m., open to the public, free of charge)

Feb. 19: vs. FC Dallas at Joe DiMaggio Sports Complex, Clearwater, Fla. (noon, open to the public, tickets via the Union’s website)

Feb. 22: vs. D.C. United at Joe DiMaggio Sports Complex, Clearwater, Fla. (7 p.m., closed)