Former world champion Button, 34, is out of contract with the British team at the end of the season and has now been told to "try harder" by Dennis.

Button is currently eighth in this season's drivers world championship standings, a huge 122 point behind leader Nico Rosberg of Mercedes.

However, Button is just 14 points in front of rookie McLaren team-mate Kevin Magnussen and Dennis, while accepting neither of his drivers, has the best car on the grid, believes the veteran Briton ought to be further in front of the Danish newcomer.

"I'm happy with the drivers in the sense I think they are giving their best," Dennis told Sky Sports on Monday.

"I'm sure Kevin is giving a big wake-up call to Jenson. In some ways you say, 'Great, we've made a great choice with Kevin'.

"But in other ways you say, 'Come on Jenson, you are a world champion and absolutely one thing you can do on a consistent basis --and you should be doing it -- is beating your team-mate'.

"Do I want him to try harder? Of course I do. He's a highly-paid Grand Prix driver.

"Yes, we are not giving him the best car; yes, it would be challenging for him to win in this car, to say the least, but he could do his bit and Kevin has to make it as difficult for him as possible."

As for the team's driver line-up for next season, Dennis said: "We want to win races and we would always hope the best available drivers would wish to drive our cars.

"The key word is 'available' because people have contracts and we respect those contracts.

"If Lewis (Hamilton) was in a position to drive for us next year, as with many of the other top drivers if they were in that position, we would love to have them on board.

"No-one should ever feel threatened, either as a driver or as an engineer. All we want to do is win and we have to take considered positions and considered decisions on that process."