With Roscommon defeating Offaly, Derry's 11-point loss means they drop to third in Division Two ahead of next weekend's final day trip to Navan and require an already promoted Galway to get a result in Dr. Hyde Park. Even then, Derry have the small matter of Meath and Gallagher could not hide his disappointment at the nature of Sunday's display against a Galway side who overpowered Derry at times.
"We had four or five players who were not playing anywhere close to the level they normally would, or that we would like and need them to be at," conceded Gallagher after the 4-11 to 0-12 defeat, "Galway just opened us up far too easily. Look, we failed a big test today and that's the bottom team.
"It was a big challenge for us but it got away from us fairly early on and it wasn't good enough. We conceded at least two goals from our own kick-out. They put a big squeeze on it and I just felt we mad a couple of very simple errors and handed them a massive initiative. It was a five or six point breeze but instead of that it ran to 12 or 13 points by giving away bad goals.
"It was something we had anticipated coming from a better quality team but we didn't react well to it and it was poor."
Derry won the toss but elected to face the stiff Owenbeg breeze, something they have done in the past, but a misfiring kick-out invited added pressure from a high pressing Galway side who had the Oak Leafers hemmed in for the majority of an opening half that finished with the Tribesmen in total control at 3-08 to 0-04
"Yeah, we decided to play against the breeze and generally do most days," added the Derry boss, "We figured if Galway came they were going to play with it anyway but it's about how you deal with it. Look, Odhran (Lynch) didn't have his best day and it created a lot of problems for us. That (lack of defensive solidity) comes from giving away those early goals which leaves a lot of uncertainty but there is not doubt they were on the front foot. They created a lot of gaps with some very good defenders coming forward as well. Listen, it was a step up in class and we were very far from the level needed."
Much of the build up to Sunday's encounter had focussed on the suspension of Shane McGuigan's after two controversial bookings in last week's draw with Roscommon was compounded by a midweek suspension. Both the harsh sending-off and the suspension took on even greater significance in light of the weekend result but Gallagher wasn't prepared to use his absence as an excuse, even if he admitted his team missed the Slaughtneil forward.
"I can't say it was in the players' head, I wouldn't expect so," he added, "It hasn't been an ideal week. You don't want your star performer sent off in the wrong but we had to park that. Obviously in the first half Shane's presence, getting an few shots away and winning a few frees, would have mad a difference but, look, you are going to be without players. He was on top of his game last week, there is no doubt about that but it is gone now.
"There is no doubt it was exceptionally frustrating. It was very disappointing, two yellow cards and I didn't think either was a yellow card but that was last week, this is this week."
Critics will label Sunday's game a reality check for Derry but Gallagher, while disappointed and frustrated, was quick to defend his team after what was a first league defeat in 13 games.
"I don't think there is that gulf or anything close between the two teams. We played Armagh and Donegal in the Championship (over the past two years) and there were two points and one point in those games. They were games that went right down to the wire.
"There is no doubt that a huge amount of those Galway players are physically in great shape. They have been doing the right thing for a considerable period of time and themselves have had a few ups and downs but we weren't good enough today and indeed far from it.
"They were very good and as soon as they turned over our kick-out they knew what to do. Likewise, they got a goal from a turnover as well. The three goals all came from us losing possession but given the quality of opposition we've been playing over the last 18 months maybe we weren't being penalised for that or weren't giving the ball away. You weren't being pressured like that. I thought Galway were physically very powerful as well and they were able to clump us in tackles and turn us over."
With promotion out of their hands, the Derry boss must now lift his players for a tricky trip to a Meath team sitting fourth of they are to have any hope overtaking Roscomon.
"I've no idea what team Galway will put out. All along it was in our hands and it is not in our hands any more," said Gallagher, "If that's the case and we are not good enough to beat Galway or Roscommon, that just might be it. Over the two games we weren't and that's what's so disappointing but today what was really disappointing was we weren't even good enough to be there with 15 minutes to go.
"There incidents when we were turned over, we deserved to be turned over. To me they weren't the right kicks. To me it's okay t go long and be simple when a team squeeze like that. Those were wrong decisions made by us on the pitch.
"We have take responsibility for that and learn from it. You notice Galway in the second half when we put a massive squeeze on, they were happy to go long and if they lost it long, and they lost an awful lot long, you're 75 yards from our own goal and you've 13 or 14 men behind the ball. That tactically, was very poor from us."