Lennon was named in Harry Redknapp's starting XI but was replaced by Jermaine Jenas just before kick-off after complaining he felt unwell.
The winger has since explained that he had been ill since the weekend and he was desperate to play in the match, posting on Twitter: "Believe me this is one game I did not want to miss and (I am) still devastated now."
He continued: "But (I) will not be made a scapegoat, saying they only knew just before kick-off.
"I fell ill on Sunday morning when the medical team put me on antibiotics, but (it) only got worse before Tuesday."
Redknapp explained what happened to the former Leeds midfielder after the final whistle, saying: "We lost Aaron Lennon a minute before kick-off, he didn't feel well, just said he had no energy, no strength. We had to change the team just as we were leaving the dressing room."
Tottenham were already trailing to an Emmanuel Adebayor goal when Peter Crouch was sent off in the 15th minute. Three second half goals - from Cristiano Ronaldo, Angel Di Maria and another by Adebayor - leaves them a mountain to climb in the second leg.
Spurs said today that Lennon will be assessed when he and the rest of the squad return to training on Thursday.
The Londoners face Stoke in the league on Saturday before the return leg of their Champions League clash four days later.
Source: PA
Source: PA