Seven weeks of R&R later, his natural optimism is back. With 11 days to the start of the season he is already trying to work out how to see all the matches he wants to.
"It's a fantastic early season," he said yesterday, as he sat in the Sir Stanley Rous room at the Football Association's Lancaster Gate head- quarters. "I'm having a problem with the fixtures, thinking, `What's the biggest game here?' Some Saturdays you pick three matches you want to go to and you are glad there is one on a Sunday and another on Monday. Then you think, `I am watching six games this week and they are all good games.' That's exciting."
But Keegan's enthusiasm is now tempered with a greater sense of the realities of his position. Yesterday he issued another ebullient rallying cry, but added a cautious rider or two.
England, he said, can be ranked within the world's elite, but much depends on the availability and fitness of players. David Seaman's calf injury, suffered in a friendly on Monday, made him the third key player on the injury list after Tony Adams and Michael Owen.
"Of course it affects me when I see Seaman coming off," Keegan said, "but it is still just over a month before I have to announce my squad. With Owen it has already gone from `He will definitely miss the start of the season' to `There is a possibility he will play'."
Once picked there is no guarantee, of course, that all the squad will turn up. "One of the things that amazes me about this job," he added, "is that you get your squad together on a Sunday night but it's Wednesday before you even have a clue of the team. There's games on a Sunday and Monday to be played so you think, `It's no good getting the players together on a Sunday night when seven or eight aren't going to be there, let's give them another day off'. But that takes another day of time that you could have preparing them.
"I would like to have a full squad to pick from, but I accept that that's probably never going to happen. I am going to always end up with about 16 of the original 22; on average about a quarter pull out through injuries or whatever."
The suspicion is that this is through overuse, with the hamstring injuries suffered by Owen and David Beckham at the tail end of last season being cited for the prosecution.
Keegan is unconvinced, but is aware that players are now being stretched to the limit. The back-pass rule and the proliferation of ball-boys and spare balls around the touchline have speeded up the game. Overseas tours, like Manchester United's recently concluded trip to Australia and Asia, may not be helping but, again, he can understand why.
"The game has got quicker. The ball's actually in play for 60 minutes but in that 60 minutes, [the players] are on the move all the time. It used to be possible to kill a game. Not now.
"You can say it is down to playing too much but sometimes if you rest players and then they come back into a game, having got used to playing game on game on game, they can do their hamstrings as well.
"They are fit boys, they are finely tuned but if you look at athletes, the difference is that they pick their matches. When Linford Christie was at his best, he would choose to miss Zurich and go to Copenhagen. It's difficult to do that with football.
"Some of the tours are because the clubs have commercial commitments, like Brazil did with Nike, and I think that's a dangerous line to go down. I certainly wouldn't want the sponsors telling me where I have to go and play.
"But we have to accept football has changed. If [sponsors] are putting vast amounts of money in they are going to make demands. Players cannot then say, `I want more money but less games'. It doesn't fit, does it? If you say to players: `Ideally, how many matches would you like in a season?', they say: `I don't want to play 60 games, I would like to play 40'. So you say, `Right, would you take a cut in wages of a third?', the answer, you know and I know, would be no."
But that was enough moaning. Problems or not, Keegan was looking forward with optimism. Even the continued influx of foreign players could be a plus.
"It may be harder for young Englishmen to force their way into a side but when they do you know you have a real England player. If Stephen Hughes [currently on loan to Fulham] gets in the Arsenal side and puts out Emmanuel Petit - that's when you know you have got an England player."
Other players are closer to selection, with the form of Chris Sutton and Kieron Dyer, following their moves to Chelsea and Newcastle respectively, of interest to Keegan.
"It's a big move for Chris Sutton, Chelsea are a club that have ambition and I want to see what he is all about in that side. I think Sutton can adapt.
"Dyer going to Newcastle is interesting one because he is now playing in the Premiership, so we won't need to guess whether he can play there any more. Kevin Phillips and Michael Gray are also back playing in the Premiership [with Sunderland]."
Further afield Keegan has already asked for a fixture list from Spain and will be booking a flight as soon as Steve McManaman gets in to the Real Madrid team.
"I am still very optimistic, I think we have had a good rest and I believe in the players, I really do. We have got work to do to justify being at Euro 2000 but we have still got that opportunity and if we qualify, we will have as much chance as anybody else. We are ranked 14th in the world now but I look at some of the teams above us and I think, `if we had to play them...'.
"I don't make any argument with Brazil, but you look at those below them and I think we are as good as anybody. I see us as a top four team in the world."