Off-spinner Moeen Ali's form is a "real issue" for England, according to former captain Michael Vaughan.
Moeen, 30, bowled only six overs on the first day of the fourth Test against Australia and has taken just three wickets in the Ashes series at a cost of 117 each.
"I wouldn't have played him this week. I don't see what he's going to offer," Vaughan told BBC Test Match Special.
"I'd have played the young leg-spinner, Mason Crane."
Moeen, playing his 48th Test in Melbourne, has made five centuries and averages 33.38 with the bat, but in this series has managed 116 runs in six innings.
Though he is an all-rounder, England need him to make a significant contribution with the ball because he is the only front-line spinner in the side.
And despite being dependable at home, he has struggled in away Tests, with his wickets coming at more than 48 runs apiece.
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Moeen was a doubt with a finger injury before the Boxing Day Test, then watched part-time leg-spinner Dawid Malan bowl more overs than him as Australia reached 244-3.
"We don't have a genuine, quality spinner," said ex-England batsman Geoffrey Boycott on TMS. "Moeen bowled six overs and Malan bowled more. That tells you quite a lot.
"They can't keep going on with a batsman who bowls a bit. You can only do that if you play a proper spinner."
Vaughan pointed to the impact of debutant pace bowler Tom Curran, who bowled impressively in Melbourne and was denied a maiden Test wicket after David Warner was caught off a no-ball.
"We saw what Curran produced," said Vaughan. "He wasn't scared of trying a few things, he had loads of life and bowled with great energy.
"What an experience for him, a young kid trying things in front of 88,000 people."
Warner was on 99 when he top-edged Curran to Stuart Broad at mid-on. The left-hander was on his way to the dressing room, only for replays on the big screen to provide a reprieve and allow him to complete his century from the following delivery.
"There's not a lot you can say in that situation," said England pace bowler James Anderson. "To see the elation when he gets one of the best players in the world on debut and then to see the screen, it's tough, it's heartbreaking.
"You've got to learn the hard way sometimes."
England, 3-0 down in the series, have already surrendered the Ashes and are now looking to avoid a second successive 5-0 whitewash in Australia - and a third in the space of 11 years.
After Australia won the toss at the MCG, they raced to 102-0 at lunch, only to be pegged back in the afternoon session.
Day two will begin with Australia captain Steve Smith 65 not out, in the company of Shaun Marsh who has 31, while England will have a new ball that is only three overs old.
"The new ball is crucial so hopefully tomorrow bodies will be fresher and we can attack them," added Anderson. "We know wickets with the new ball are crucial because the pitch will get slower.
"We were ruthless in the second session and didn't give them much to hit so need more of that tomorrow."