Diallo, 35, joins up with former Dons boss Martin Allen at Whaddon Road to continue his recovery from a summer shoulder operation.
"It's a good opportunity for me and just what I needed," he said.
"I missed pre-season because of my injury and when you have a new manager to play for that can be very frustrating.
"I've been working hard to get fit, but you need regular football to really get your fitness back and I have the chance to do that now.
"I know Martin Allen well and he knows my strengths too, so I'm looking forward to working with him again."