W/O looking anything up, I'd say no to the first and yes to the second. This is because the first specifies a lack of concentration to be the the limiting factor, but the second doesn't - so the inability could be caused by any mental disablement of which lack of motivation is a feature.
However, going back to the first, in this context is there really a difference between lack of concentration and lack of motivation? If someone lacks the motivation to engage in the activity in the first place, will they really have the concentration to sustain it?
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