Martin Johnson says hooker Steve Thompson will be a key man if the Lions are to win in New Zealand this summer.
The England and Northampton forward faces competition from Shane Byrne, Gordon Bulloch and Andy Titterrell for a place in the Lions' Test side.
"I think Steve Thompson is one of the key guys for them - he needs to be in good form," Johnson said.
"He can do a lot of things that other players can't do in terms of his ability with the ball."
Johnson captained the Lions to victory in South Africa in 1997 and was also skipper in 2001, when they were beaten by Australia.
He added: "It would be nice to see him at his best, running with the ball for the Lions. It would give them another card to play."
Captain Brian O'Driscoll and fly-half Jonny Wilkinson will also be crucial players for the Lions, according to Johnson.
"Obviously Brian O'Driscoll is captain and there's a focus on him," Johnson said.
"He's an absolutely outstanding player and it would be great for the Lions if he was in his best form.
"If Jonny Wilkinson is at his best he offers some things that probably no-one else there can do, particularly defensively and he's very experienced in the big pressure games.
"But certainly there's enough players there to cover anyone if they are not at their best."
Johnson retired from international rugby after leading England to their 2003 World Cup triumph.
And he ended his club career captaining Leicester to a heavy defeat by Wasps in the final of the Zurich Premiership play-offs last weekend.
But Johnson, who has signed for new sports legend company Nobok, will be making one final appearance at Twickenham in his testimonial game, the Nobok Challenge.
He will lead a northern hemisphere side against a southern hemisphere team led by All Black star Jonah Lomu.
He admitted it would be strange when the game was over and he would not be playing rugby any more.
"Suddenly there is no training to go to on a Monday and no game to think about on the Saturday so it is a bit weird," Johnson said.
"Maybe after the match we'll see how I feel but probably not until next year and I'm not playing and not involved it will sink in a bit more then I think."