England shun Pietersen due to breakdown in trust
South African-born Pietersen is England's highest run-scorer in all forms of international cricket.
"Now is the time for some really open and honest conversation," Strauss told Sky Sports television.
"He's been a phenomenal player for a long period of time [but] it's not about his ability as a player. It's about trust. You can't build that over a few days.
"I went to see him last night to let him know he is not part of our plans for this summer. I can't give him any guarantees about the future but he is not banned from the side because no-one knows what is going to happen in the future."
Pietersen, who has scored 8,181 test runs, was sacked by England after their 5-0 Ashes whitewash defeat early in 2014 and it seems he has little chance of returning for the five-test series against Australia that starts in July.
The South African-born Pietersen and former England skipper Strauss were team mates for a long time but also have something of a chequered history.
The swashbuckling middle-order batsman was dropped for a test against South Africa in 2012 after sending provocative texts about Strauss to the opposition.
Former Middlesex opener Strauss was then forced to issue an apology in July 2014 after being caught on microphone making offensive remarks about Pietersen while on a commentary stint with Sky.
"The trust isn't there at the moment. I wish it wasn't the case but it is the case," Strauss said on Tuesday. "If there's a way to build trust let's look at it... this isn't about Kevin Pietersen, it is about the future of English cricket."
"No-one has ever doubted Kevin Pietersen's ability as a player, he has been a phenomenal player for England over a long period of time and his record stacks up to anyone in England cricket and he should be very proud of that record.
"But over months and years the trust between himself and the ECB [England and Wales Cricket Board] has eroded and we are in a situation now where there is a massive trust issue between Kevin and I," Strauss added.
"If there is a way to build trust let's look at it but at the moment we are quite estranged. I know from my time playing cricket for England that trust is absolutely imperative in any team environment."