Shearer, the former England football captain, this week agreed to put his planned retirement on hold and play another season for Newcastle United in the role of player-coach.
Johnson declared himself unavailable for the Lions tour to New Zealand this summer - but had he not done so, it would have been tough for Sir Clive Woodward to leave him behind.
The Leicester man quit the international scene after leading England to the World Cup in 2003 and will hang up his boots from the club game at the end of this season.
And nothing will change his mind.
"In a lot of ways it's a very easy decision to make because you know when it is time. I knew when it was time with England and I know when it is time here," he said.
"I am enjoying it. We will get as far we can get and win what we can, if we can and at the end of the season I will retire.
"I am not like him (Shearer). It's only three months to the start of pre-season, and I will not be there, believe me."