PORT Adelaide captain Travis Boak is not injured, but is struggling for form, says Power coach Ken Hinkley.

Boak has cracked 30 disposals just once this year, against the lowly Brisbane Lions last week, when he had 31.

Going into Sunday's clash against Carlton he was averaging just over 23 touches per game, but he could only manage four kicks and eight handballs to have little influence on the contest.

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Hinkley has been adamant all season that Boak is fit.

"I'm sick of the question to be honest," Hinkley said.

"Trav's not playing ripping footy. There's nothing wrong with him. I don't know how many times I can say it to people. I get asked week in, week out.

"Travis is just not in form, consistently. He's been building. The last couple of weeks he's been a bit better for us, but today he was not on his own when he didn't have a great game."

Boak's prime form won him selection in the All Australian team in 2013 and 2014 and the Power will be hoping he can return to his best in the coming weeks.

Hinkley acknowledged Carlton's better players as being decisive in the Blues' two-point win at Etihad Stadium on Sunday afternoon.

"Crucial times, crucial moments, their leaders stood up for them," he said.

Hinkley said the narrow loss came down to the Power not being good enough when it counted.

"We led for lots of the day and put the game in a position where we shouldn't have lost it. We just weren't strong enough at the end," he said.

WATCH: Ken Hinkley's full post-match media conference

A win would have had put the Power in the top eight, but now they sit at 4-4 ahead of next week's tough home clash against West Coast.

"It's a big game to lose. Forget all the external stuff – coming into the game, it was probably a line-ball game (based) on both sides' form," Hinkley said.

Jackson Trengove's role in the ruck limited the Power's ability to restrict Carlton in attack.

The Blues lost Levi Casboult to injury in the first quarter but they were nevertheless able to dominate marks inside-50 (17-6).

Casboult is 11th in the competition for marking the ball in the forward 50.

"You're trying to figure out match-ups that work," Hinkley said.

"We probably just gave them too much room at crucial moments. If we had have shut their space down a bit earlier, maybe they wouldn't have marked as many balls."