The 24-year-old winger, who had a spell at Hull last year, will stay at the club for six weeks.
Manager Neal Ardley told Dons Player: "Toby is a lad who I watched a couple of times at the start of the season and I tried to get him into the Under-21s set-up when I was at Cardiff.
"However, Bristol City had already made a move for him prior to me watching him.
"They signed him on a short-term deal until January, but I think they are now in the process of trying to tie him up longer term because he has done so well.
"Toby is a player with pace who can play on either flank or up front. He is what we need as he can bring more pace to our attacking play."