By North-west correspondent Tony Hughes

Roberto Martinez needs to sign a defensive coach in the summer to keep his Everton job, according to Stan Collymore.

The Goodison Park manager is under mounting pressure in the wake of a campaign that has not lived up to expectations.

Martinez is widely regarded as having the best Everton squad for many years at his disposal, with emerging stars Romelu Lukaku, Ross Barkley, John Stones and Gerard Deulofeu supplemented by experienced pros like Phil Jagielka, Gareth Barry, Seamus Coleman and Leighton Baines.

But Everton dropped to 12th in the Premier League table following Sunday’s 1-0 defeat against Manchester United.

With billionaire Farhad Moshiri buying a majority stake in the club last month and planning to make major investment in the squad in the summer, there is growing speculation that Martinez’s job is under threat.

“Bill Kenwright and Moshiri should act now with Lukaku,” former Liverpool striker Collymore wrote in The Mirror. “They should be on the front foot, sitting him down and outlining their plans. They should be telling him that they will splash out on top players and build a team round him, which will make the Champions League a viable and ­regular target.

Farhad Moshiri has sold his stake in Arsenal for £200million to buy Everton

Money man: Moshiri is most important person at Everton after buying 49% stake

“And they should be telling Martinez to go and get himself a defensive coach – or risk losing his job. I’m not advocating ditching Martinez because he’s got plenty of good ­qualities, but he needs to sort that defence out and, if it still isn’t working by Christmas, I’d bullet him.”

Everton have conceded 42 goals in 30 Premier League matches this season, a ratio that is outdone by only 13th-placed Bournemouth and the bottom four clubs.

In other Everton news, Romelu Lukaku’s father Roger has urged his son to consider quitting the club for one of Europe’s elite clubs.