Sydney FC's Siem De Jong injured scoring winner vs. Wellington Phoenix

Siem de Jong's winning goal may have come at considerable cost as Sydney FC beat Wellington Phoenix 1-0 to maintain their push for top spot in the A-league.

The Sky Blues' seventh win in their past eight games lifts them within a point of Perth Glory but coach Steve Corica's immediate concern will be the fitness of marquee man De Jong.

The former Netherlands international was injured in the process of scoring his 25th-minute goal from close range, writhing for several minutes on the goal line holding his left knee.

Problems mounted soon afterwards when midfielder Anthony Cacares hobbled off with a calf complaint, continuing a patchy campaign for the Manchester City loanee.

Corica said De Jong's status was unclear.

The 29-year-old fell awkwardly when clipped by Andrew Durante and will definitely miss Saturday's match against Melbourne Victory. Beyond that is uncertain.

"Siem was obviously hit from behind and he heard a crack so I'm not too sure of the damage," Corica said.

The injuries took the gloss off a display in which the Sky Blues frustrated a Phoenix side whose club-record unbeaten run has ended at nine matches.

The hosts had a chance to level through a contentious penalty awarded when Sydney defender Michael Zullo clattered into Steven Taylor.

However, Roy Krishna's penalty was saved by Andrew Redmayne preventing the in-form Phoenix striker going top in the golden boot race.

A draw would have flattered fifth-placed Wellington, who struggled to break down a Sydney FC defence which was vastly more structured than during the shock 3-1 loss when they met in round seven.

Phoenix coach Mark Rudan surprised by resting playmaker Sarpreet Singh and it was his second-half introduction which provided creativity but not the goal they craved.

Corica was pleased with his team's discipline while Rudan believed a draw would have been a fairer result but wouldn't criticise Krishna's modest penalty attempt.

"Roy normally steps up and buries them. It's just one of those things," he said.

"We had enough chances to get ourselves back into the game and had we scored that penalty, I was really confident we could push on for the winner."

De Jong's goal came via an indirect free kick, when a stretching assist from Aaron Calver left him to prod home from close range.

He collapsed to the turf in the same motion, leading to a lengthy treatment period and slow exit down the tunnel.

Sydney were unfortunate not to be two-up at the break, after Phoenix fullback Louis Fenton appeared to commit a blatant handball inside the box.

Referee Daniel Elder didn't change his initial non-penalty ruling after viewing a replay of Fenton's clumsy efforts with a bouncing ball.

Both Corica and Rudan felt a penalty was warranted.