Michael Murphy must be Donegal's key weapon against the "Achilles' heel" that is Dublin's full-back line, according to former All-Ireland winner Bernard Flynn.
The Meath legend believes that is the Ulster side's only hope of dethroning the All-Ireland football champions when the counties meet at Croke Park in this Saturday's quarter-final (throw-in 6pm, live commentary on RTÉ Radio 1 and on RTÉ.ie).
"Donegal will definitely have to zone in on the Dublin full-back line from the start, I think that's their Achilles' heel," Flynn told RTÉ Sport.
"Play Murphy inside and go the long ball early on. Stay in the game and be there with 10 or 15 minutes to go, that's the number one thing they have do.
"They need to be aggressive in their tackling and disciplined in their defence. They were very poor against Cork defensively.
"Those are the two areas, tight defence and go long and test the Dublin backline, where they're weak in the air."
Flynn concedes, however, that even that may not be enough to see off the well-oiled blue machine, whose power and pace he backs to eventually triumph over Rory Gallagher's side.
"We know what we're going to get from Dublin, they need a bit of a test and this is going to be it."
"We know what we're going to get from Dublin, they need a bit of a test and this is going to be it," Flynn said. "They won't particularly like playing Donegal.
"If you have two man-markers on Connolly and Brogan, and if they have an off-day, then Donegal have a chance. But I think Dublin are just waiting to get out there.
"They are bursting at the seams to get out in Croke Park, to strut their stuff and really put a marker down against Donegal and blitz them early on.
"I think Dublin's running game and those power plays off the shoulder at pace, Donegal must stop that at source.
"But it's going to be very hard to do that. Dublin have the best forward unit and running game in the country so I think they'll win by a few points."
The opening game of the quarter-final double header at headquarters sees Tyrone facing a Mayo side that has struggled to fire on all cylinders this season.
Their victory over Westmeath was overshadowed by a near collapse in the second half that allowed the Lake County to reduce a 12-point lead to just three, and Flynn argues that such a drop in intensity cannot be repeated if they are to challenge for a semi-final place.
"Mayo's lapses in concentration - they must stop that and they must start really well," Flynn said. "They must get much more aggressive and go back to that hard, firm tackling that they are really good at.
"Tyrone, off the shoulder, running at pace, I'm looking forward to their young players coming to Croke Park. I think it's going to be a fascinating game but something tells me Mayo have a real chance.
"They won't fear Tyrone at all and have more experience than a lot of Tyrone players.
"Tyrone were in trouble against Donegal for long periods, so if Mayo can really improve on their lapses in concentration and get really aggressive, play on the edge and come back to that firm disciplined tackling then I think they've a chance."
