BBC tennis pundit John Lloyd says Andy Murray "may have to play the best match of his life" to reach the final of the Australian Open.
Murray faces world number one Novak Djokovic in Friday's semi-final, the man who beat him in last year's final.
"Murray has to stay with him and break him down and be aggressive and serve well," Lloyd told BBC Sport.
"He's got to fight and if he gets down believe he can turn it around because Djokovic is not going to give an inch."
"It's great to have the 'Fab Four' [Djokovic, Rafael Nadal, Roger Federer and Murray] in the semi-finals; they've taken tennis now to a different level.
"They've demolished the field at the Australian Open.
"They've shown that they are a class above everyone else and we're lucky to have them; if you get those four in the semi-finals how can you ask for more than that?
"There have been some great eras and you look at the [Jimmy] Connors, [Bjorn] Borg, [John] McEnroe era - that was pretty special as well - but this one is tough.
"If and when Murray wins his first one - and I think he will - it will be an amazing achievement as he's playing against three players who will certainly be in the top 10 of all time by the time they finish their careers."
"I thought he should have gone with Jimmy Connors - he's gone with [Ivan] Lendl but it was the same type of thing.
"He has to have someone in his corner who's been there and done it. Lendl has won Grand Slams and is quite frankly a better player than Murray is at the moment.
"In the past in critical stages Murray has lacked a little bit of respect for his coaches.
"He wouldn't say that of course, but he's sometimes given them a little bit of stick. I don't think he will do that with Lendl. I would be surprised if he does and if he does it will be interesting to see what Lendl's reaction will be."
"When Murray gets in tough positions he's got to say: 'You know what, I am out there on my own. It's not my coach's fault, it's not my camp's fault, I've got to take responsibility for my actions'.
"There's no problem with getting angry on the court. I think Murray said that sometimes you've got to let it out. I agree 100% with that but when you get into that feeling-sorry-for-yourself mentality, not only is it bad for him but it also helps the opponent.
"When a Nadal or Federer or Djokovic see Murray going through some of those periods when he starts moaning, it feeds them. They love that and you cannot afford to do that.
"The differences at this level is such that you cannot afford to give anybody a present.
"He can correct that, but it's not going to be easy to do it.
"It comes down to the mind. It's the toughness. How much do you want it? How tough can you be when the points keep going on and on and on in the heat, and you are looking across the net and this man is just coming at you the whole time?
"You've got to compete at that level the whole time, you cannot drop it.
"Some matches in Grand Slams he's almost like a little boy in comparison to those guys, who are men. Now it's time for him to step up and prove that he can compete at that level for five sets in Grand Slam semis, and finals if he gets there.
"I think he can and I hope Lendl will be the difference."
"I've got to go for Djokovic. I just think the way he played last year and the way he has come into the Australian Open, I've got to go for him in four sets.
"But I think it's going to be one heck of a match and, with the Lendl factor now with Murray, who knows...maybe that will help to tip it in Andy's favour."