Celtic have seven fixtures - including the League Cup final and Old Firm derby - before 3 January.

"We're having to play a ridiculous amount of games," Postecoglou said.

"I guess it's the way and manner which we play our football. It's very demanding on the players.

"We don't have the squad yet to cope with that. That's putting stress on us, which we've had to deal with it pretty much the whole way through.

The Scottish Premiership side took an early lead in their final Europa League game through Stephen Welsh's header.

But Betis levelled twice following a spell of three goals in five minutes - including Ewan Henderson's strike with his first touch - before David Turnbull's decisive penalty earned a 3-2 win.

Postecoglou said Ajeti's injury "looked fairly significant" but is awaiting the prognosis of Kyogo's issue, with the Japanese forward forced off in the second half after replacing Ajeti before the break.

The manager had changed his entire starting team in order to protect players, and was asked pre-match if the intensity of their preparation would have to reduce.

"No it's not possible," he responded. "It's just a by-product of the team we want to be.

"It's nothing that's new to me or unexpected. I've been through this process a number of times with teams I've taken over and the initial stages are always challenging for everyone and you just try to mitigate the risk as much as you can.

"But obviously games are coming thick and fast and we don't have the depth we need right now. We're probably putting players under undue stress but that's the levels we want to be at."