Chelsea interim manager Guus Hiddink revealed Friday he had concerns regarding Belgium playmaker Eden Hazard's form and fitness.

Hazard was booed by a small number of Chelsea fans when substituted during Wednesday's 2-1 home defeat and 4-2 aggregate reverse against Paris Saint-Germain that saw the Blues crash out of the Champions League, having angered supporters at Stamford Bridge by swapping shirts with PSG's Angel di Maria at half-time.

Hazard's father was quoted as saying in the Belgian press this week that his son's injury problems dated back four months to when former manager Jose Mourinho was in charge of Chelsea but that he had been obliged to play on.

"His father made a fair judgement. He is not absent of injury," Hiddink said ahead of Saturday's FA Cup quarter-final away to Everton.

"What is an injury? You can have an injury where you cannot play, or where you can play when you are not fully fit," the Dutchman added.

"I have my concerns about him as well: whether he should play, when he's not top, top fit, an hour at full intensity or another part of the game (as a substitute). We're trying to help him.

"He will be available (against Everton). He's desperate to participate in a team performance."

The root cause of Hazard's injury problems remains something of a mystery and Hiddink said: "I try to exclude a lot of emotion in that and see whether his working radius is okay. The intention he is doing in training and in the game, it's not what you think. You think sometimes 'oh, he's not doing enough'. That's not true.

"We have to find another entrance to get him on this level. Working harder is possible, but not with stupidity. Or maybe one or two days off might help.

"Every now and then I see that he (Hazard) is capable of doing beautiful things, very efficient things. We try to help him and find a path where he can grow and it's a different approach for everyone."

Chelsea captain John Terry is back in contention for this weekend's trip to Merseyside after six matches out with a hamstring problem.

"He worked rather well the past days. I would like him to travel to Liverpool," said Hiddink.

Terry scored an equaliser in the eighth minute of stoppage time to earn a 3-3 draw with Everton in a Premier League clash at Stamford Bridge in January.

The central defender won the FA Cup in 2009 during Hiddink's first spell as Chelsea caretaker manager and the Blues boss is keen to lift the trophy again, although ensuring last season's Premier League champions continue to climb up the table from their position of 10th place remains the priority.

"It's a very important cup to go for," Hiddink said. "But you have to focus also on the Premier League and not neglect that."