Alastair Cook admitted his frustration at being unable to reveal why England have decided to move on without Kevin Pietersen but thinks there are "a huge number of reasons to be optimistic for the future".
Pietersen was part of the England team whitewashed 5-0 under Cook's leadership in Australia during the winter, but was left out of the squad for the recent World Twenty20 and will not play for England again.
What led the England and Wales Cricket Board to axe Pietersen has since been the subject of much speculation, but the settlement agreed between the two parties is the subject of a confidentiality agreement - for the time being at least.
Cook, speaking to Sky Sports News at Essex's pre-season media day, was asked about the Pietersen decision and said: "I can't actually answer that question totally at this precise moment in time, which is incredibly frustrating for me.
"Everyone will say I'm sitting on the fence. There are a number of reasons which will become clearer soon but you have to respect the position I'm in at this precise moment. I know everyone is going to keep asking that question until we give the answers but at the moment we just can't.
"The decision was not taken lightly, without a lot of consideration and thought... It was a tough decision and will be made clearer in due course."
England had won the previous three Ashes series, including at home in 2013, before unravelling on their tour Down Under.
Cook accepts England are now entering a rebuilding period, which will start when a permanent successor to Andy Flower as head coach is appointed in the near future.
"The winter that's just gone in all forms of the game has been very disappointing," he said.
"You look back and think 'what could we have done differently?'. In hindsight, you'd change a few things of course but, at the time, the planning and preparation hadn't changed from what we'd been doing in the summer.
"The Test side that got us to No 1 (in the rankings) and won three Ashes series in a row probably won't play again, it's broken up quicker than we'd all imagined. But that provides an opportunity for guys to put themselves up for selection.
"It is the start of a new era and we're waiting on the appointment of a new coach. When that decision is made then you can build.
"The county championship season starts next week and gives everyone a great opportunity to put their name forward.
"For a long time we've had a settled team but when a side breaks up and you aren't successful then places are up for grabs.
"Any player who scores a lot of runs and takes a lot of wickets will put their name forward for selection. There's a lot of very good cricketers out there who want that England shirt."
Limited-overs coach Ashley Giles is among the candidates to replace Flower, who decided to stand down after the Ashes defeat but will remain with the ECB in the newly-created role of technical director of elite coaching, based at the academy in Loughborough.
Giles' cause was not helped by England's failure to make the semi-finals of the World Twenty20, ending with an embarrassing defeat to the Netherlands.
Cook, not part of the T20 squad, has previously worked with Giles in his role as ODI captain and described him as a 'fantastic coach and man'.
"There were a lot of very good things which were marred by what happened in that last game," said Cook of England's World Twenty20 campaign.
"That's incredibly frustrating. Gilo, like everyone, has had a tough winter. He's a very, very good coach.
"There are a lot of important decisions to be made by the (ECB) hierarchy over the next couple of weeks. I know there are a number of good candidates we can choose from and Gilo will certainly be in the frame.
"I don't make that decision. The coach-captain relationship is very important and I have an input, but the final decision is with the ECB board.
"Ashley is one of the favourites because he knows the system well and I've enjoyed working with him.
"Those decisions will be made over the next couple of weeks. It's an exciting time for English cricket and we have to look forward. It's been an incredibly tough winter, we can't hide away from that, but there's a huge number of reasons to be optimistic for the future."