He had just attended a board meeting rather than the routine training session. In the aftermath of Celtic's 6-1 collapse against Barcelona a comparison came to mind of an errant schoolboy summoned to the headmaster's office. The reality was prosaic. "It was nothing to do with Wednesday night, thankfully," Lennon said. "I'm still here . . ."
The manager has had the sort of week in which friends and family looked at him with soft, sympathetic smiles, as though he was ill. That's what happens when your team crashes like his did in Camp Nou. Lennon has endured bad defeats and embarrassments before as Celtic manager but never with a scoreline as heavy as that. For what it's worth, he felt losing 4-0 to Utrecht in 2010 was worse, that result sending them out of Europe.
The Barcelona defeat was humbling for Lennon because he sat on the bench feeling powerless and fearing a seventh or eighth goal. "Obviously we're all sore, and disappointed with the way the campaign finished," he said. "But we set ourselves a very high bar last year and we weren't able to replicate it for varying reasons. We lost, or sold, three very good players and for me we were in the toughest group. Financially we are way, way out of that league. We can compete in footballing terms; we can't financially.
"I thought we probably wouldn't be as strong [in the Champions League this season]. Look at Victor Wanyama; there's not a conveyor belt of Wanyamas out there that you can find one every year. They don't come along that often. People might say we struck lucky with him: we found a good player, we developed him and we sold him for a lot of money.
"That is the strategy I have been told to work in. Find players with resale value, develop them and sell them on, and in the meantime try to be as successful as you can on the pitch. We've had two back-to-back campaigns in the Champions League. We had no real right to qualify for the last 16 last year but we did. Maybe we overachieved last year. To go again, after losing those three players, was always going to be a difficult thing to do in this group. Even if we'd had those three players I'm not convinced we would have qualified anyway?"
The basic assumption is that spending money equates to automatic Champions League progress but Juventus, Benfica, Napoli and Shakhtar Donetsk are all out of the tournament having spent multiples of Celtic's transfer outlay.
The other aspect of Celtic's campaign was the failure of existing players to live up to the standards set by the team in reaching the last 16 a year ago. Lennon was scathing about their performance in Camp Nou but did not write them off in terms of having a future at the club.
"I think there is more to come, there can be an improvement in the players who have been here for a few years and certainly in the players that have come in. Virgil van Dijk has done exceptionally well, I think there's more to come from Derk Boerrigter, Teemu Pukki and Nir Biton. Amido Balde is a work in progress but I have maintained that all along. He was basically a player we wanted to bring in and develop and eventually make better. That's still going ahead.
"Gary Hooper didn't come in as an automatic Champions League player when he joined us. Neither did Wanyama or [Adam] Matthews or [Mikael] Lustig. So maybe they need a bit of time before we can go again. The main thing is to make the Champions League and have a go at it from there."
Matthews felt Celtic had gone into Wednesday's game with "false confidence" after three close matches against Barcelona. "That's a huge mistake, I wasn't aware of that," Lennon said.
One of the greatest concerns for Celtic in midweek was the general flatness and timidity of the performance, as if the players found it difficult to motivate themselves in the knowledge they already had been eliminated from Europe.
That raises the question: if they cannot be motivated for a game against Barcelona, what chance is there of them lifting themselves for routine fixtures such as today's home SPFL Premiership match against Hibernian? The European result and the absence of the now dispersed Green Brigade are certain to have an impact on the crowd. "We have to create our own buzz again," Lennon said. It will have to be done without Boerrigter, Charlie Mulgrew and James Forrest who are all injured.