Agostino returns for Adelaide

United' home match against Phoenix looms as an early season danger game for the Reds as they prepare for a hectic month of football.

With a FIFA matchday break next weekend, the Reds know three points against Phoenix are of utmost importance as the squad prepares to play five games in 16 days, comprising of three Hyundai A-League matches and two AFC Champions League quarter-finals matches, which includes one in Japan.

United coach Aurelio Vidmar is aware that a win over Phoenix will have his team in a positive position heading into a demanding September schedule.

"It is a must-win game. If we can win this one we will go into the break in a really good position," Vidmar said.

Bolstering United's chances on Saturday is the return of striker Agostino and midfielder Diego to the main training group.

Agostino is in line for an immediate call-up while Vidmar said Diego would probably need another week to be considered.

Veteran defender Michael Valkanis has also been named in an extended squad.

"He (Agostino) was probably ready last week but we were just a little bit precautionary with him so he's ready to go," Vidmar said of his marquee signing.

"It's pleasing to have Diego back training because he adds a lot to our team. He's still lacking a bit of match fitness and he pulled up a bit sore after yesterday's training, so he will probably miss out this week."

The last time United played Wellington, Agostino scored in a 2-1 win, the match starting an impressive run for the striker as he scored a further three goals in the next two games.

The Reds' only injury concerns are Olyroo Kristian Sarkies, who is a week away after suffering a minor knee injury at training last week, and Cassio, who continues to improve from a calf injury.