Former England captain Kevin Sinfield has been warned he will be a 'target' when he makes the switch to rugby union at the end of the season. Sinfield, 34, the greatest captain in Leeds' history, stunned the world of rugby league on Tuesday with his sudden announcement that he will quit the sport at the end of the season and join the Rhinos' sister club Yorkshire Carnegie on an 18-month contract. Leeds Rhinos captain Kevin Sinfield is to switch codes and join Yorkshire Carnegie at the end of the season . Castleford head coach Daryl Powell, the man who made Sinfield captain at the age of 22, trod the same path, although in a coaching capacity after losing the Rhinos top job in 2003, and has a word of warning for his former team-mate. 'It surprised me a little bit,' Powell said. 'It will be interesting to see if he can make a success of it but he's been an outstanding player and captain within the sport and you wouldn't back against him. I think he's been unbelievable in his career. 'He won't need my advice. He knows what he's doing. I'm sure he will have done all his homework. Sinfield (centre) lifts the Super League trophy after Leeds beat Warrington in the grand final in October 2012 . 'It's certainly a challenge. You look at Sam Burgess and what he's going through, and Iestyn Harris - it's tough. It's not an easy thing to do. 'The one thing you do have is a bit of a sign on you, on your head. You're a bit of a target. 'It's a completely different sport. It will be interesting to see what position he's going to play, but I wish him all the best.' Sinfield is tackled during a match between Leeds Rhinos and Leigh Centurions last year . Sinfield, who has guided the Rhinos to six Super League titles, three World Club Challenges and the Challenge Cup in 2014 at the expense of Powell's Castleford, will be the second high-profile departure from Headingley at the end of the year following Jamie Peacock's appointment as Hull KR's new football manager. The former Golden Boot winner is closing in on third place in rugby league's all-time scoring list with 3,997 points, but Powell believes his old club have a ready-made replacement in 20-year-old Liam Sutcliffe, who has deputised for an injured Sinfield in the last two matches. 'They've got some really good young players,' Powell said. 'Liam Sutcllife has slotted in there and seems to be doing a good job. He looks like a mature young player who can handle things pretty much the way Kevin did when he was a young fella. Sinfield (left) in action for England against France during the 2013 Rugby League World Cup quarter-final . 'I was obviously at the back end of my career when Kevin started and it looked like he was going to be an outstanding player. But I don't think anyone could have foreseen how good he was going to be and how many things he would win and how much he would grow as a leader in the game. He's been awesome.' Sinfield has been named in Leeds' 19-man squad for Friday's derby at Castleford, but coach Brian McDermott will not rush his skipper back. 'I'm not sure if he's going to be fit for Friday,' McDermott said. 'What we have got to make sure when Kev does come back into the team is that he's 100 per cent fit. 'Sutcliffe's played really well in these last couple of games. He's held his own and in some parts of the games has played really well. 'It's good to know that while Kevin's in recovery, Sutty is doing a good job and getting more experience.'
Kevin Sinfield has announced he is leaving Leeds at the end of the season .
The 34-year-old will cross codes to join sister club Yorkshire Carnegie .
Former England captain has won six Super League titles with the Rhinos .