Alastair Cook admits there is ongoing concern in the camp about Matt Prior's return to fitness ahead of the Test series against Sri Lanka starting in June.
England claimed an emphatic victory over Angelo Matthews' side in the 3rd Royal London One Day International at Old Trafford on Wednesday to take a 2-1 series lead with two matches remaining.
They were hoping to be able to call upon the services of Prior when the Test series begins next month but the 32-year-old's recovery from an Achilles injury has been slower than expected.
"It is a big concern," Cook said.
"I've been speaking to him every week, and he's been doing everything he can. He's incredibly frustrated, because Achilles injuries are hard to heal.
"He's a big part of our plans, but we can't rush a guy back. That wouldn't be fair on him or to the England team.
"There's time, about two weeks to the first Test, and we'll be in constant communication throughout.
"He knows he is a big part of things, and we want him to be there. But if he's not there, it will give someone else an opportunity."
Johnny Bairstow played for England in the final two Ashes Test matches in Australia at the turn of the year when Prior was dropped mid-series.
England's limited-overs wicketkeeper Jos Buttler, who has taken seven catches in three ODI's against Sri Lanka this tour, will hope he has done enough to dislodge Bairstow as Prior's replacement in the Test side.
Cook admits Buttler is a talent, but insists the 23-year-old has a long way to go in order to become an England regular at Test level.
"Like a lot of guys, he is a really talented wicketkeeper and a really talented cricketer," Cook said.
"He's nowhere near the finished article with his wicketkeeping. But just watch him practise - you will see him put the hard yards in - and that will keep going the right way, no doubt."
Cook was delighted by the manner in which England beat Sri Lanka at Old Trafford and feels the visitors, who were dismissed for just 67, were not expecting such a fast start from his side.
"As a sportsman, you have to spend your time ... looking at the next challenge and bouncing back from the bad stuff," he said.
"I think we caught Sri Lanka napping a little bit. We were out of the blocks straightaway."
You can watch the fourth ODI between England and Sri Lanka live on Sky Sports 2 on Saturday at 10am