McGregor finally re-entered the cage in July to rematch Max Holloway after a five-year layoff but suffered a knee injury seconds into their clash after attempting a jumping kick. McGregor said he was “confident†after undergoing knee surgery in August, and Aldo would suggest not coming back as a welterweight.

“Yeah, I think first he needs to go through some dietary re-education to see if he can get back down and be lighter again,†Aldo told MMA Fighting. “I think, in my opinion, he has the frame for 155, so it would be good. And I'll tell you this: today, if Conor fights at 155 and beats a name [that isn't necessarily at the top], the division is wide open again. To me, the division has kind of stalled there. Ilia [Topuria] moved up and lost to [Justin] Gaethje, so it's a bit of a mess there, and anyone can come in and snatch the title.â€

McGregor became the undisputed featherweight champion when he knocked out Aldo in December 2015, and that was his final fight at 145 pounds. The Irishman jumped around between 155 and 170 pounds since then, winning the UFC lightweight belt in the process, and even hinted at fighting at middleweight one day.

Prior to the injury, McGregor's coach John Kavanagh said that “170 is a comfortable cut for him now and he's got the frame for it,†and it would require “something really big†to make sense to once again cut extra 15 pounds for a UFC fight.

“His frame has also gotten much bigger, he's gained a lot of weight and muscle mass, so we don't know what he's going to be like when he comes back,†Aldo said. “But I always hope for the best, so I hope that tomorrow he's doing well physically and psychologically, too, and that he can return to the UFC and have great fights again.â€

Aldo has history with both Holloway and McGregor, fighting them in three UFC title fights at featherweight, and was disappointed to see their highly anticipated rematch end that way.

“Regardless of the outcome back when we fought, I always root for everyone to be able to fight, come back, and do their job,†Aldo said. “It's sad because of the injury. Everyone waited for him to come back, and then he comes back, you have that fight week, everyone is excited, millions and millions of people [tuning in], and then when the time comes, that happens. It's sad. I think it could have been a great fight, him and Max, but he got injured. It's sad, you know? I hope he can come back, recover, and return to the octagon.

“We don't know if he'll come back in his prime, if he'll come back at a high level, considering how much time he's been away. I think he was out for two years, or four, I don't remember, and then he came back, got injured, and now he's going to be out for even more time.â€