England v Sri Lanka, 1st ODI, The Oval June 27, 2011

One-day job is Cook's biggest test

England's third captain in eight days has a tough task to secure results for the team but also convince about his own one-day credentials

Alastair Cook has shown he is a cricketer who likes a challenge. Nine months ago his struggles in Test cricket brought his place into question, but he has since responded emphatically with six hundreds in ten matches including an Ashes series that brought 766 runs. Now he faces one of his biggest challenges; turning England into a one-day international force before the next World Cup and proving himself as a 50-over batsman.

Cook starts at The Oval, on Tuesday, against a Sri Lanka team strengthened by one-day specialists and buoyed by their Twenty20 success as he becomes England's third captain in eight days. He has, by far, the toughest job of the trio. Strauss, despite his recent lean run, is secure of his position while Stuart Broad, a left-field choice for Twenty20 captain and without any professional leadership experience, has fewer expectations on his shoulders.

If Cook achieves his twin tasks of team and personal success it will be a result to equal what he achieved in last winter's Ashes series. It will also smooth the path towards the Test captaincy but, despite being groomed as Strauss's heir apparent, if his one-day role goes seriously wrong he could yet fall down that pecking order.

"I just see myself as the one-day captain," Cook said. "I'm only concentrating on tomorrow's game and doing the best job I can. We can worry about the other stuff later. We are very separate in what we do and it's a huge honour for me to lead this one-day side forward."

Cook, however, begins his spell as full-time ODI captain having to prove himself on two fronts both as a leader and a limited-overs batsman. It is the latter which raises the most questions with a current record that reads an average of 33 and a strike-rate of 71. He is in this side because he is captain but, currently at least, there are other players in the domestic game (and even in his own squad, such as Ian Bell) who could comfortably rival him for an opening spot.

There are many who feel strongly that he isn't the right man, with one of most vocal critics the former England captain Mike Atherton who called Cook a "plodder" on a Sunday morning TV show. "Takes one to know one, I suppose," was Cook's response. "Everyone has their opinions. I have scored a one-day hundred for England and I'm excited I can score runs at the top of the order. I know I can score runs quickly, but of course I'll have my own style of doing it."

It is now Cook's job to develop into the role, and for encouragement that it can be done he need look no further than the man he has just replaced. Strauss was never one of the finest one-day players in the world - although his 158 against India, at Bangalore in March, was one of England's finest one-day innings - but he expanded his game to ensure he was never a passenger.

Strauss's return to the side in 2009 in the West Indies has echoes of Cook's current position because no one was really sure that he was the right man. Strauss was made one-day captain by default after the Kevin Pietersen-Peter Moores fall-out, but earned the Player-of-the-Series award in a 2-1 series win to show he was worth a place. What Cook would give for a similar series now.

"He can be a great example for me," Cook said. "When he first started playing one-day cricket he was striking around 65 but by the end he was around 80. So you can develop as a player and he showed that. Hopefully I can follow in his footsteps."

For doubters over Cook's pedigree as a one-day batsman, and also as a captain, there is evidence that he has it in him to become a success. Many things that happened on the Bangladesh tour in early 2010 were important for English cricket - not least the emergence of Steven Finn and Tim Bresnan's development of reverse swing - but Cook was very impressive as Strauss's stand-in.

It's easy to diminish the achievements because of the opposition, but England have since lost twice to Bangladesh in one-day internationals so Cook's unbeaten tour now looks a good achievement. And he scored runs, too, both in Tests and ODIs. In the three-match one-day series he out-paced Craig Kieswetter, with whom he will be reunited at the top of the order against Sri Lanka, as he made 156 runs at 52 with a strike-rate of 90.69. A limited sample size, admittedly, but something to build on.

"I think my one-day game has evolved since I last played. In Bangladesh I scored runs and scored them quickly so I know I have the talent and skill to do it," Cook said. "Of course I'm nowhere near the finished article, I'm 26 years old, I've got a lot of work to do and I'm prepared for that."

Cook has a lone six in one-day internationals, but that came in Bangladesh where he developed an effective slog-sweep over midwicket which proved how he is willing to move out of his comfort zone. One concern, though, is that a return to one-day cricket, where playing with an open face to third man is a regular shot, will undo all the hard work of tightening up his technique for the Test game.

But English cricket needs to find out now, with the best part of four years until the next World Cup, if Cook is the right man and he certainly couldn't want for better form. "That's part of the skills you need to have, the ability to change your mindset from one-day to Test cricket," he said. "We all need to do that and get better at it."

However, if things do begin badly in the next few matches Cook would again do well to look to Strauss who was whitewashed 5-0 by Sri Lanka in 2006, in his first full series in charge, when Michael Vaughan and Andrew Flintoff were injured. A poor start does not have to be terminal, but while the next 12 days won't define Cook's captaincy career the next 12 months will have a major say.

Andrew McGlashan is an assistant editor at ESPNcricinfo