John Terry has warned his team-mates that two former Chelsea stars will be determined to get revenge on Jose Mourinho at Everton on Saturday.

Blues boss Mourinho sold Romelu Lukaku to Everton for £28 million ($46 million) in the close-season rather than give the powerful Belgian forward a chance to compete for a place in the Chelsea team.

Lukaku had already spent last season on loan at Everton and Mourinho off-loaded the 21-year-old with a few choice words about his lack of motivation.

That brought a barbed response from Lukaku about not feeling wanted at Chelsea, setting the stage for a potentially explosive first reunion at Goodison Park if the striker can recover from a toe injury in time to start.

And, even if Lukaku doesn't feature, Chelsea are likely to come up against Cameroon striker Samuel Eto'o, who joined the Toffees this week after being released by Mourinho at the end of last season.

Eto'o has insisted he has no ill feeling towards Mourinho despite an awkward relationship in the second half of last season culminating from a joke about his 'real' age that was caught on camera and broadcast, but he would clearly love to mark his Everton debut by showing he can still cut it at the highest level.

Terry is aware of the potential danger lying in wait and he said: "We've struggled away to Everton in the last couple of years.

"With that in mind we know it's going to be tough. Obviously big Rom (Lukaku) will be up front as well, with a point to prove, him being sold from the club.

"And they are going to be up for it; they always believe they can turn us over at home.

"It's a big test for us, but we go there with a one-game-at-a-time mentality, and try and move on from there."

Everton manager Roberto Martinez is not worried about Eto'o's physical fitness despite his lack of match action since last season.

"I would have loved Samuel to have 10 or 11 sessions before we put him in a competitive environment but I learned quite quickly I was wasting my time," Martinez said.

"He wants to be helpful to the team straight away, he wants to be involved.

"And Romelu has a very strong inner motivation and he isn't motivated by who he is facing and who is in front of him, it's more about his role and status at Everton.

"He's vital for us, he's enjoying that and I'm excited about his performances."

While Blues defender Terry ponders the challenge he will face this weekend, an injury to Diego Costa has been shown not to be as serious as first feared as Chelsea look to maintain a 100 percent start to their Premier League campaign.

Costa suffered a muscle injury in a training session on Wednesday but tests although confirmed it was a minor one the man who struggled with a hamstring problem at the end of last season may require time to recover.

Mourinho will have to decide whether the Spain striker can play any part against Everton.

A first start in his second stint at the club for Ivory Coast striker Didier Drogba appears likely therefore, especially as the future of Fernando Torres is uncertain as the Spain striker is understood to be keen to complete a move to AC Milan in the next few days.

Everton's on-loan Chelsea midfielder Christian Atsu can not face his parent club, while South African winger Steven Pienaar is definitely out with a groin injury and Ross Barkley, Bryan Oviedo and Arouna Kone are also absent.