But Arena was able to cobble together some workarounds by pairing a couple of old parts with a new one, sparking a 4-1 victory over D.C. United in the regular-season opener for both teams.
Mike Magee, returning to the Galaxy after 2 1/2 injury-plagued seasons in Chicago, came off the bench in the second half and played a big part in all four goals, scoring two, assisting on one and drawing the penalty that led to another. Defender Daniel Steres, in his first MLS game, also had a goal and reserve goalkeeper Brian Rowe made five saves to shut out United after entering the game in the 20th minute.
That's not exactly the way Arena drew it up during a busy off-season in which he acquired a goalkeeper and three big-name European stars on defense. So he'll head back to the drawing board this week carting a victory earned more with resolve and determination than sheer talent.
"It's a good kind of win for us, that we had to come from behind and dig a little bit," he said. "Bringing in a goalkeeper in the first half, highly unusual. We dealt with some issues and overcame them."
The Galaxy's season wasn't even six minutes old before its new defense cracked, with Lamar Neagle putting D.C. United up, 1-0. He got a lot of help on the play from the Galaxy's Steven Gerrard, who had his pocket picked by Neagle and Chris Rolfe, starting a counterattack that ended with Neagle slotting a left-footed shot past Dan Kennedy and into the lower corner at the far side to unleash a cascade of boos from the crowd of 25,667.
That would be the only shot Kennedy would face in his long-awaited Galaxy debut, with a leg injury forcing him to join bruising center back Jelle Van Damme, another of Arena's key off-season acquisitions, on the sidelines. Van Damme didn't even suit up because of an injury.
Midfielder Giovani dos Santos was the next to hobble off, yielding to Magee to start the second half. And Magee didn't wait long to make his presence felt, setting up Steres for a header in the 54th minute to tie the score, 1-1.
"He didn't do a whole lot," Arena said, jokingly. "In all seriousness, that's the reason why we wanted to bring Mike back here. We think he's a great player and can score goals."
The goal ended a 387-minute scoreless streak in preseason and CONCACAF Champions League games for the Galaxy, and it came only seconds after the team was frustrated on two spectacular chances: the first when a Robbie Keane header one-hopped the crossbar and the second when United goalkeeper Andrew Dykstra juggled and held a Gyasi Zardes' header from close range.
That only delayed the evitable, though, with Magee scoring the deciding goal 11 minutes later, taking a cross-goal pass from Sebastian Lletget on the left side of the penalty area, settling the ball with his left foot, then volleying a soft right-footed chip into the net at the far post.
In the final 10 minutes, he won a penalty kick, which Keane converted, after Dykstra knocked him down in the box before closing the scoring by nodding in a Gerrard free kick.
"It feels a little bit surreal," said Magee, whose last goal had come in August 2014. "I didn't know what to do when I scored. Once the game it ended it felt weird and incredible.
"I'm still scrambling for words."