Ryan Crotty has been a reliable player for the All Blacks in recent seasons.

Ryan Crotty remains undecided about his playing future in New Zealand.

As overseas clubs continue to net first and second-tier players during the pre-World Cup cycle, NZ Rugby will be alert to the danger of losing All Blacks and Crusaders midfielder Crotty.

Over the past fortnight NZ Rugby has re-signed All Blacks loose forwards Jerome Kaino and Steven Luatua, but lost their grip on Charles Piutau.

Then came the news Colin Slade, who like Crotty and Piutau is gunning for a place in the All Blacks' World Cup squad, was being chased by French club Pau.

Crotty, like Slade, is off-contract after this season and his ability to play both midfield positions, training ethic and durability will be of major value to a northern hemisphere club.

At 26, Crotty is in the prime of his career.

He has made 13 test appearances since his debut against the Wallabies in Sydney in 2013, amassed 88 Super Rugby caps for the Crusaders and was preferred ahead of Malakei Fekitoa on the bench for the All Blacks' tour finale against Wales in Cardiff last year.

"Like anyone in my position I would weigh-up all opportunities and decide what's best for me and my family," Crotty said when asked if there was potential for an offshore move.

"It's interesting that a lot of players are taking up those offers but I guess everyone is different. They have to do what is best for them and their families. Colin is a great friend of mine and whatever he does I will back him."

It's not only NZ Rugby that will be worried about the future of Crotty, who will be expected to sack Fekitoa on the drift defence during Saturday night's match at AMI Stadium.

The Crusaders will also be desperate to keep hold of the player who debuted for them in 2009. Losing players close to the scrum is fast becoming a concern.

Five-eighths Dan Carter and Tom Taylor have already signed for French clubs and if Slade departs it would leave wider training group player Richie Mo'unga as the organisation's most senior playmaker.

Halfback Willi Heinz won't return from his broken leg, having agreed to join English club Gloucester. Andy Ellis, such a key figure for the team, is also off-contract and may look outside New Zealand after completing the second year of his deal with Japanese club Kobe Steelers.

Flanker Richie McCaw is also expected to retire after leading the All Blacks at the World Cup.

Farewelling Crotty, who has also captained the Crusaders, would exacerbate concerns about shedding so many experienced men in the backline but there are fewer concerns in the pack.

Forwards Kieran Read, Matt Todd, Sam Whitelock, Luke Romano, Owen Franks and Jordan Taufua are all contracted - as is fullback Israel Dagg - beyond 2015 and Wyatt Crockett has indicated he wants to stay.

Tighthead prop Franks, 27, will be keen to record a win against the Highlanders for his 100th Super Rugby match.

Even when taking the long trip back from South Africa, and jetlag, into account the Crusaders have listed as the TAB's favourite to beat the southerners.

Crotty warned that the 52-10 win over the Sharks in Durban last weekend was against a side who, defensively, were exposed by analysis.

"African teams defend really tight around the ruck which gave us the opportunity to play wide. I think New Zealand, dare I say it, are maybe a little smarter defensively in how they preview teams and are not as habitual as South Africans."