'Make Steve Bruce feel uncomfortable' – Longstaff brothers issued Newcastle United challenge
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The pair have found themselves out of favour at United in recent times, having started the year as the club’s first chosen Premier League central midfield pairing.
And Clark thinks the onus is on the players to get their heads down.
"If the manager isn't picking them, then they have to force his hand, every day in training make sure they are the best midfield players on show and make it difficult for Steve Bruce to leave them out,” said Clark.
“I've been on both sides of it. I've been a player in that position where you're trying to prove yourself. We had a really strong group of midfield players at the club when I was there and you had to convince the manager to put you in the team.
“And I've also been the manager where you're on the other side of it and what you've got to do is make the manager feel uncomfortable, in terms of the fact that he is leaving you out and it leaves him a little bit embarrassed because you've performed great in training and when your getting your opportunities from the bench or the occasional start, you're the best player. That's how you have to look at it.
“Any successful club has competition for places because if you don't have that then players become complacent. If your position is under threat then automatically you've got to give it everything you've got to keep your place in the team.”
Both players were linked with deadline day moves away from Newcastle – but Clark thinks they did the right thing in staying put.
“I'm not surprised that Matty and Sean stayed,” he told Tribal Football.
"It is tough, it is their local team and they want to do well. But they've got to get their heads down and work hard. Obviously there is another addition in (Joe) Willock to come into the midfield area, so they've got a fight on their hands to get their place.”