The Spain international was left on the bench for the first leg of the Champions League semi-final last night.
Instead, boss Luis Enrique started Jeremy Mathieu on the left-side of what turned out to be a wafer-thin defence.
The move backfired as Juve stormed into a 2-0 half-time lead through Paulo Dybala.
Steven Gerrard was shocked not to see Jordi Alba start for Barcelona
Gerrard believes Alba should have started ahead of Mathieu
Enrique subbed Mathieu off at the break with Andre Gomes coming on – but by that point the damage had been done.
Gerrard, speaking on BT Sport, said: “I can’t understand why Jordi Alba is on the bench.
“I don’t know if he’s carrying a bit of a knock but it’s a big surprise to us that he wasn’t in the starting XI.
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“Juventus have found Barcelona’s weakness very quickly.
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“Mathieu is having a nightmare at left-back. He’s not getting tight enough, he’s backing off and he’s scared of Juan Cuadrado’s pace.”
Fellow pundit Steve McManaman agreed and said: “The left and right side of their defence is all over the place. They’ve been terrible.”