Former Bundesliga player Vidosic was absent from the Reds' teamsheet for Sunday's 1-0 loss to Perth Glory and was sorely missed in Adelaide's struggle.

Coolen said that after a series of pre-season injuries since his move from Germany's FC Nuremberg, an untimely illness on the eve of the new season forced Vidosic out of the side.

"When he came with us, the first weeks, he had some problems with his knee, so he took two weeks off to recover from that," Coolen explained.

"Then he had some little problem with his calf, because of the hard pitches so he never got a lot of sessions in a row, and finally he was fit, and then he got sick.

"So a little bit of unlucky moments. We have to work on his fitness. Hopefully he will be back in the squad next week.

"He's still not fit for a full game but maybe he can come off the bench or maybe he can start part of the game."

Having impressed at Brisbane during the 2006-07 season, Croatian-born Socceroo Vidosic moved to Nuremberg in Germany.

The last two seasons saw him loaned out by Nuremberg to MSV Duisburg and Arminia Bielefeld before his return to the Hyundai A-League.

Despite Vidosic's talents, Coolen said he still had work to do fitting in with the squad.

"He has special qualities of course, but also you have to understand that you have to work in our shape and the way we prefer to play," Coolen said.

"But having a player available like Dario Vidosic ... we are looking forward to having him in the squad. It gives you more flexibility and possibilities."

As for his side's performance in the season opener against Glory, the coach was happy with an improved second-half effort, even if his side were torn apart during the opening period.

"We were, I think, very lucky at half-time we were still 0-0," he said. "Perth were much better than us.

"We changed it in the second half. We played a little bit different system, different formation (that) gave us a lot more stability in the midfield.

"The second half, I think we turned over the game, we controlled them. We didn't create a lot of chances, but we were much better than Perth the second half.

"I think they scored in the period that goal, when they were not playing well, we were on top of them. That happens in football and they scored a goal."