Keith Curle admitted there are no guarantees he will be able to strengthen Carlisle United's depleted defence despite Tom Parkes' opening-day injury.

The Blues rearguard is now down to its last four fit players after debutant Parkes suffered an ankle injury in the defeat to Swindon.

The ex-Bristol Rovers and Leyton Orient man is having the problem assessed and United will desperately hope it is not serious.

Curle said that, "ideally", he would be able to bring in extra players if needed.

But United's tight budget could rule out immediate additions.

The Carlisle boss said: "We have got a few reinforcements that we've been monitoring. We're aware that situations may change game by game.

"Ideally we'd get people into the building but sometimes that can cause another problem in itself.

"What we do want is players of the quality we're looking for, and we try to bring in players who are better than we've got."

Asked if he had started the season with too few defenders in the squad, Curle said: "If that's just aligned at centre-backs, no.

"We have to also look at the younger players we've got in the building - some of the youth team players…one door closes another opens and how that opportunity comes about, you never know.

"You might have youth team players being given the opportunity, grabbing it with both hands and going on and furthering their careers. That can happen."

Curle also said he had faith in Mark Ellis if the previously out-of-favour centre-half now gets his chance.

The former Shrewsbury man came off the bench to replace Parkes on Saturday and could start at Fleetwood in Tuesday's Carabao Cup first round tie.

"I've got to say that Mark, not only as a player but as a professional, his character, has been absolutely excellent since he's come back into the building after his loan spell [at Forest Green].

"He is desperate to do well, desperate to be part of it and desperate to play."

Curle - who said United were still waiting to learn exactly how they will benefit from the sell-on clause in Brad Potts' move from Blackpool to Barnsley - admitted his squad was "down to the bare bones", with four other players still sidelined.

"Jason Kennedy is back on the grass on Monday, then it will probably be the beginning of next week when he's able to join in training with us," Curle said.

"John O'Sullivan's going to be a while - he's going to go down to see a specialist and have an operation on Monday.

"Kelvin Etuhu is starting his rehabilitation on the grass on Monday, and is probably 10 days to two weeks away. With Samir Nabi, I'm hopeful that by the middle of this week he'll be back doing football-related training on the grass."

Curle felt United did not get the benefit of ref Andy Haines' decisions in Saturday's 2-1 reverse, in front of a 6,036 crowd at Brunton Park.

He felt Luke Norris' opener for Swindon may have been offside, while Carlisle's players insisted Paul Mullin had punched the winner into their net.

But Curle also admitted Carlisle had made "stupid" mistakes and added: " All teams will make mistakes, including Premier League players and internationals.

"We will learn from them very quickly and move on.

"You don't win or lose the season on the first game. There are bits and pieces that I'm not happy about that we can improve on, but there were also some positives to come out of the game."

On Carlisle's opening-day defeat after several weeks of build-up, he added: "It's like Christmas morning - you're that excited, the build-up's there, you know you're getting presents, you get little sneak previews of them, you know they'll all be under the tree when you wake up, then you get a little big startled because you haven't got the bike that you wanted."