Diagouraga joined Leeds United from Championship rivals Brentford earlier this month.
Scottish Championship outfit Rangers were interested in the 28-year-old midfielder, according to a report in The Scottish Sun earlier in January.
The Scottish Sun had also quoted Diagouraga as saying that he would be interested in working with former Brentford manager Mark Warburton at Rangers.
However, it is Leeds who snapped up the Frenchman, who is regarded as one of the better midfielders in the Championship.
Former Rangers midfielder Ferguson, who is considered a legend at Ibrox, believes that Diagouraga would have been a good signing for the Gers.
“Of course, it would have helped him if the board had signed Tounami Diagouraga from Brentford but that didn’t go his way either so Warburton must be feeling pretty frustrated all round right now,” the former Scotland international has written in The Daily Record. “I’ve spoken to a few people about Big D and he would have been a sensational signing.
"He’s at a good age with plenty of experience and would have been the ideal man to fill that position but Leeds came up with the cash that Rangers weren’t prepared to pay and as a result Warburton has lost out on one of his top two targets.”
Diagouraga made his debut for Leeds against his former club Brentford away from home at Griffin Park in the Championship on Tuesday evening.
The former Peterborough United midfielder played the final 31 minutes of the game and had a pass accuracy of 92%.