Gatland said earlier this month: 'Sam feels he could play now. He has made some really good progress and is really happy with how he has responded to treatment over the last few weeks. I expect him to play before he goes to New Zealand.'
But, despite the early optimism, the decision has been taken to hold the Lions captain back from any competitive action until the start of the 10-match tour, which kicks off against New Zealand Provincial Barbarians on June 3.
"The medical staff are very happy with Sam's progress but they will not risk him aggravating the injury before the start of the tour," a well-placed Lions source told Sportsmail.
"His recovery is going really well but the risk associated with him playing for the Blues is considered too high for him to take a chance.
"There have been some mixed messages about whether he will play for the Blues again this season. But to be clear, he definitely will not."
Warburton's absence will be a major blow for Blues supporters who had hoped he would feature in their European Cup play-off against Stade Francais on Friday.
But it may be a sensible move to ensure he has every chance of being fit for what is expected to be a gruelling and attritional Test series in New Zealand.