Younis joins United from NSW Premier League club Apia Leichhardt Tigers, where he has scored 17 goals from 22 appearances this season.

United coach Aurelio Vidmar believes Younis will slot in well at the club and expects the 22-year-old to form a formidable combination up front with proven goal scorers Paul Agostino and Cristiano.

"Robert will be a great addition to our squad," Vidmar said.

"He is a proven goal scorer in the NSW Premier League and after watching him in the trial game against Para Hills, we think he has what it takes to go to the next level, to back up Cristiano and Paul Agostino as the squad's third striker."

Younis found the back of the net in United's trial match against local Super League club Para Hills last week and is excited about getting his chance in the A-League.

"I'm really excited, it's a dream come true and I'm looking forward to the challenge of playing in the Hyundai A-League and proving I can play, especially after the faith Aurelio Vidmar put in me," Younis said.

"Adelaide United has a good foundation, there are a good bunch of guys here and I look forward to being part of a successful club and the first team to have made it into the second round of the AFC Champions League."

Younis will join United's squad following his commitments with the Apia Leichhardt Tigers.