He's playing. Klopp said well before the break that he's in a good way and doing full training, and made the good overlooked point that keeper training is intense. With a lot of quick repetition of the actions required that are affected by his calf, like diving and instantly getting up for another and like kicking at range. Not to mention usual aerobic fitness.
If he's getting through these repeatedly, and was doing so before the break, he's almost certainly ready for 90 minutes which aside from a few focused moments won't have the same intensity as a couple of full sessions.