The Chelsea midfielder has been recovering from an Achilles injury suffered at the end of last season prior to the Europa League final.
But after training normally this week, Lampard can call upon the box-to-box midfielder once more.
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“Ruben is in the squad,” Lampard revealed. “He’s not fit to start, but great to have him in the squad.”
Though N’Golo Kante, who hobbled off in the 2-0 loss to Manchester United, will face a spell out with a thigh injury.
“N’Golo is not fit,” Lampard added. “It’s a muscle injury, similar to the one he came off with against Arsenal recently. Hopefully three weeks, something around that.
The Blues boss will not be able to call on Christian Pulisic for a while yet, but Tammy Abraham could return from an ankle problem, while a broken nose for Andreas Christensen will not prevent him from lining up after travelling to Milan to have a protective mask fitted.
“Pulisic is still not fit. I can’t give you an exact date. It’s a difficult injury and we’re working on that,” Lampard added.
“Andreas went to get a mask for a broken nose, which he has now got and has trained with. He’s available for selection, albeit with a mask.
“He’s trained two days at a good level, where there has been contact and heading to do. He’s been playing so well; Andreas is in great form.
“We will have to see if he’s ready, because this is going to be a battle and as a centre-back you need to be confident you can take contact.
“Tammy has trained the last two days probably at about 70 per cent having not trained much recently,’ concluded Lampard.
“He’s in the squad but I’ll have to make a decision on whether he’s fit.”