Both forwards played a key role in England's recent Six Nations triumph, with Eddie Jones steering the Red Rose to a first Grand Slam since 2003.
Johnson highlighted other contenders for second row when the Lions tour Australia in 2017, but believes that Itoje and Kruis will "take some shifting".
"Paul O'Connell has gone but Alun Wyn Jones is still there, while Ireland are excited about Iain Henderson and Scotland's Richie Gray is working on his fundamentals. I think Eddie Jones has handled Maro's rise very well, first using him from the bench and then getting him into the starting lineup. The guy is only 21 and is already being heralded as a saviour of the game," Johnson told lionsrugby.com.
"Let's let the kid play. I could see from watching him at club level that he was a fine athlete - at a level which we might not have seen in the second row before. But I was worried he was more of an athlete than a rugby player. Does he have that natural instinct for rugby? Quite clearly we can say now that he does. Hopefully he can be managed properly by club and country and England can have him not just for 2019 World Cup, but through 2023 to 2027.
"Having said all that about Maro, George Kruis has just quietly gone about his business and got better and better with every game. They make a fantastic pairing - their lineout under the guidance of Steve Borthwick was very impressive and they are going to take some shifting between now and the Lions tour."
Johnson led the Lions to victory in the 1997 tour of South Africa.