ET exclusively spoke with the 45-year-old actor on Thursday, where he addressed speculation that it was him who threw out the life-sized cardboard cutout of the actress. Photos of a man placing the cutout in the trash surfaced shortly after news broke that Ana and Casey's brother, Ben Affleck, had called it quits. The pic shows that it's the same cutout Ben's three children -- Violet, 15, Seraphina, 12, and Samuel, 8, whom he shares with ex-wife Jennifer Garner -- placed in front of Ben's house over the summer.
"No, that's not me, and I can't even really say if they have totally broken up for good or whatever. I would leave that to them to speak to," Casey told ET's Rachel Smith. "A bunch of people sent that picture to me and I was gonna tweet some, like, joke, response or something. And then I couldn't think of one and a joke didn't seem appropriate. And I don't have Twitter so that wasn't going to work. But it definitely wasn't me."
"The reality is, I think that this year has been really hard on people in relationships. I wouldn't know because I've been single, but I bet there are a lot of people that have, you know, it's been challenging to relationships," he continued. "And I think that Ana is just the sweetest, funniest, smartest, most charming person. I think she won't have any problems meeting somebody else."
Casey also raved over Ana's acting skills, going so far as to predict that she'll "win an Oscar next year."
"I saw her performance as Marilyn Monroe in this movie called Blonde, which hasn't come out, and I would bet a lot that she's gonna pick up every single award," he explained. "She's gonna have a good year. I'm not too worried about her."
"I think she's a catch in every way. And I'll be there to carry Ben through it, but I don't think he'll have any problems [either]," he added. "My advice to them would be like, 'Yes, think long and hard about it, because quarantine is not fun if you're single.'"
When asked if Ana and Ben could reconcile, Casey told ET that he has "no idea," but will "be sorry if it doesn't work out."
"I think she's really, really great," he raved. "People don't know her too well because she hasn't, like, been out there [in the spotlight] for so long. But she's just incredibly sweet, such a sweet person and so talented."
Of course, Casey has his own talents to be proud of. The Massachusetts native is starring as journalist Matthew Teague in Our Friend, in select theaters and on demand Friday, Jan. 22. He told ET that the plot -- along with an all-star cast that also features Dakota Johnson and Jason Segel -- was one of the factors that drew him to the role.
"First of all, I loved everybody involved," he said. "It's a true story about a family that's in crisis and they have this old friend who drops everything in his life to come and help kind of get them through it. I don't know what other people would say about what the meaning of the movie is or whatever, but for me, I liked the message that if you need a friend, be a friend, you know? If there's nothing, there's no better way to feel, to lift your own spirits, than to show up for someone else in a totally selfless way. I loved that. It's a little bit like that old show Highway to Heaven but Jason Segel plays the Michael Landon part [of Jonathan Smith]."
Casey added that it was extremely beneficial having the real-life Matthew Teague on set as executive producer.
"I liked him. He was really supportive and he's a nice guy," he shared. "Anytime I had a question, he would tell me. Sometimes I got the sense that he was looking at me like, 'Boy, that ain't me,' but I didn't mind. I told him from day one, it's not going to feel like looking in a mirror when you're watching this movie."