The September international window is in the rear-view mirror, which signals a crucial period for U.S. men's national team players abroad.

With Mauricio Pochettino declaring that September camp was his last chance to experiment ahead of the World Cup, the pressure is on players to impress with their clubs ahead of October friendlies against Australia and Ecuador.

That includes players who are taking their first steps at new teams. Several World Cup roster hopefuls made their debuts over the weekend, with one player in Germany particularly under the microscope.

We'll start this week's Five with Gio Reyna's mixed Borussia Mönchengladbach debut.

Reyna impresses, Gladbach falls flat

The most anticipated debut from a USMNT standpoint came at Borussia-Park, where Gio Reyna finally took his first steps as a Gladbach player with a start against Werder Bremen.

The results were decidedly mixed. From an individual standpoint, Reyna's debut was about as encouraging as could reasonably be expected from a player making his first start in more than six months.

The 22-year-old had a number of moments that emphasized his tantalizing potential, nearly tallying an assist on a first-half through ball and maintaining or advancing possession skillfully several times.

The problem? Gladbach looks like an absolute mess. Reyna's new side fell 4-0 to Bremen, with manager Gerardo Seoane sacked on Monday following a 0W-1D-2L start.

Seone's replacement will likely see film of Reyna's debut and conclude that the USMNT midfielder should be part of the solution moving forward.

Agyemang proves a handful

Patrick Agyemang's debut for Derby County had to wait a month, but the hefty striker was as advertised in an impactful cameo off the bench.

After making the move from Charlotte FC, Agyemang missed Derby's first four games with a hernia surgery.

The USMNT striker made his Derby debut against West Brom on Saturday, coming on in the 69th minute. He quickly showed why the Rams paid a reported $8 million for his services, stretching the game and using his large frame to bully defenders.

The coup de grâce came in the 84th minute, when Agyemang got a crucial headed flick to find Andreas Weimann in the box. The forward kept his composure, finishing low to seal a 1-0 win for Derby.

“Patrick today was great for that 20 minutes when he came on,” Derby County manager John Eustace said after the game.

Musah steps into Atalanta spotlight

There isn't a whole lot we can extrapolate from Yunus Musah's Atalanta debut, but the early signs are at least promising.

Musah subbed on in the 76th minute of Atalanta's 4-1 home win over Lecce, with the match very much in hand by the time he entered.

The good news from Musah's perspective was that he replaced Marten de Roon in central midfield, seeing out the final 15 minutes playing as a No. 6 (incidentally, that is his new number as well).

After he was moved all over the pitch during his time at AC Milan, finding regular minutes at his best position would be a major boost for Musah.

Pepi back in a big way

When Ricardo Pepi starts for PSV, he tends to score.

So it proved on Saturday, when the striker netted a brace in his first start of the season. Pepi has been gradually worked in after a serious knee injury last season, missing USMNT duty this month as he built up his fitness.

The break seemed to do Pepi some real good, as he scored twice in PSV's 5-3 win over NEC Nijmegen.

Per Opta, Pepi has now scored in all nine of his PSV starts since the start of last season, totaling a ridiculous 16 goals in that span.

McKennie returns to Juve XI

Pochettino's explanation for omitting Weston McKennie from his roster this month never seemed to entirely add up.

"We already know Weston, it's not necessary to call him," Pochettino said. "We wanted to give him the possibility to be more settled in his club and have the possibility to be in his best form."

But the coach hadn't seen McKennie since the spring, and the midfielder has played just four times since he took over the USMNT. And it isn't as if McKennie is at a new club and needs time to adjust.

Whether Pochettino was being completely straightforward or not, it appears that staying with Juventus over the international break was beneficial for McKennie.

After making late cameos in Juve's first two league matches, McKennie started Sunday's Derby d'Italia against Inter. He went 79 minutes, playing slightly out of position on the left flank as Juve secured a wild 4-3 win.

McKennie was solid, if unspectacular in the win, but has at least appeared to further ingratiate himself into new manager Igor Tudor's plans.

This article originally appeared on Pro Soccer Wire: The Americans Abroad Five: Reyna headlines several USMNT debuts

Reporting by Seth Vertelney, Pro Soccer Wire / Pro Soccer Wire

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