Barlow and his wife Dawn's baby Poppy was delivered stillborn last month and Williams has said that they are going through the "heaviest thing".
The 'Candy' singer spoke of his sadness upon hearing the tragic news, but said that Barlow will be able to get through it eventually.
"You know, Gaz is the most solid man I know, way more solid than me," he told The Sun.
"He has the ability to put things in compartments. But this is the most testing thing he's ever had to go through, I'm sure.
"It's just one of those things where we'll see how it goes when I see him, but it's obviously a very, very sad time for both him, Dawn and the kids."
Williams said that he has yet to talk to Barlow in depth about the baby loss, but that he hopes to do so in the near future. The pair met up at the recent GQ Awards, where they both received trophies.
"It's the heaviest, heaviest thing, and, like I say, Gaz is so together. We'll sit down and have a proper chat at some point but so far it hasn't happened.
"We're at an awards ceremony, it's not the place to talk about anything. It was very much surface stuff. But we shall be spending time together soon."
Robbie Williams is currently expecting his first child with wife Ayda Field, and spoke about how the actress is doing as she nears the birth date.
"She's been confined to London. She's not supposed to be due until the 26th.
"Ayda's like a very slim girl with a basketball — from the back you can't tell she's pregnant. She has been like an athlete where being pregnant is concerned — she's been a machine.
"The first trimester she was nauseous and the second was amazing. Then the third trimester was pretty similar up until last week.
"Then she had a couple of days of full-on grump, which is only to be expected when your bladder is the size of a pea and a human is treading on your insides.
"She got diabetes through it too, so she's had to watch her diet. But she has been absolutely f**king amazing, because I know that hormones get the best of people."
Williams recently said that he is hoping to make a return to Take That in the future.