McLaren have admitted that they are lining up drivers to fill their two seats for next season, amid intensifying speculation over the future of their current lineup.

Fernando Alonso and Stoffel Vandoorne are not contracted for 2019, leading to increasing talk on who will be racing for the struggling team next season.

Alonso, still considered by fans, pundits and fellow drivers as one of the most talented drivers in the paddock, has stuck with McLaren since 2015, despite being part of a team that has consistently failed to give the Spaniard a competitive car.

His clear frustration at a lack of progress has led to constant speculation that the two-time world champion is looking for a seat at a team at the top-end of the grid, though nothing has opened up for him yet.

It remains to be seen whether Alonso will even stay in the sport past the current season, having dabbled in other forms of racing recently, notably Le Mans and Indianapolis 500, as he attempts to win the Triple Crown of Motorsport.

Vandoorne on the other hand, is at the opposite end of his career, having made his full F1 debut with McLaren in 2017.

After an encouraging start to life at McLaren last season, the young Belgian has endured an inconsistent second year with the team, leading to doubts over his future.

And now McLaren chief, Zak Brown, has only added fuel to the fire by stating that the Woking-based constructors are looking to draw up a shortlist of drivers for next year.

"We do have a long-term agreement with Fernando and Stoffel but in these contacts there's a variety of elements to them," he said, per Sky Sports.

"We will make our driver decision when we're ready, and anticipate that being some time after the summer break.

"We're still reviewing, analysing, what we think is ultimately the best line-up for McLaren moving forward."

Among those potentially being considered is Renault driver Carlos Sainz.

"We think Carlos is an excellent racecar driver," Brown said. "Of course Carlos is potentially on the market, I don't know his exact situation at Renault and Red Bull but he's certainly someone as you go down the shortlist of drivers that you'd consider putting in your car.

"If he was free, and if we had a seat, he would certainly be high up the list for a racing seat."

The move has become more of a possibility since it was revealed that Esteban Ocon is set to sign for Sainz's current employers.

Despite the praise for Sainz and being on the lookout for new drivers, Brown was also quick to defend Vandoorne, saying he was "very much part of that consideration", but speculation continues to mount about his future.

This comes after the 26-year-old has been unable to out-qualify veteran Alonso in his second F1 season, not scoring a single point in the process.

Another driver in the frame is junior driver and F2 front-runner Lando Norris, who McLaren are keen to use in order not to lose to a rival team.

"We want to keep Lando in the family," confirmed Brown, although he is also concerned about a young driver pairing if McLaren continue to struggle on the track.

Brown added: "We're waiting to see ultimately what Fernando wants to do, because it's also about the package - experience and youth - especially in the situation we're in where we're rebuilding.

"To have two young drivers with a difficult car wouldn't be a good place to be. If we had a better car, then you might take a risk with two younger drivers.

"In situations like this you need to keep every door and every avenue open and wait for some dominoes to fall. You've got to watch them all.

"We're not prioritising one over the other. We know our situation with Stoffel and we're seeing what other opportunities may or may not be available.

"Reality is that we have two open seats, and it's our job to get the best driver situation possible and that requires talking to other drivers up and down the pit-lane."

One or two moves in the F1 driver market always have the potential to spark other moves across the paddock, and only time will tell if Alonso gets one last dream move in his career and if McLaren keep the faith with Vandoorne after a tricky season.