Hibernian will be without central defenders Liam Fontaine and Darren McGregor for lengthy spells as the duo are treated for leg injuries.
Fontaine, 31, needs an operation on an ankle problem sustained playing for Hibs' under-20s, while McGregor, 32, is recovering after Monday's knee surgery.
Describing Fontaine's injury as "a real blow", head coach Neil Lennon said: "It is a lot worse than we thought.
"It's similar to the injury he had last year. He'll be out for 10 to 12 weeks."
Lennon said a scan showed a ligament in Fontaine's ankle had "come away from the bone" and revealed that McGregor could be missing for four to six weeks.
Speaking before Motherwell's visit to Easter Road on Saturday, Lennon said: "The rest of the squad is healthy. We have good depth in the squad. If Ryan Porteous is called upon he will be ready, I have no qualms about him.
"Efe Ambrose and Paul Hanlon were excellent last week so I'm hoping for more of the same."
Meanwhile, speaking at the end of a week in which Celtic were outclassed 5-0 by big-spending Paris St-Germain, Lennon argued that Scottish clubs are still capable of defeating far wealthier opponents.
Five years ago, Lennon, in his first tilt at the Champions League group stage, famously guided Celtic to a win over a Barcelona side featuring Lionel Messi and Andres Iniesta.
"I don't see why not," said the Northern Irishman when asked if such a result could be repeated.
"When you are a Scottish team in the Champions League you need to have your best players available.
"[Celtic manager] Brendan [Rodgers] has had some problems at centre-half. First of all they have done really well in qualifying and they are doing okay domestically but it catches up with you eventually.
"No [Moussa] Dembele, and for those games he is a big miss. Hopefully when the players are fit you will see Celtic make inroads in the games."
Lennon says the task for him and other managers in the Scottish game is to ensure teams with bigger budgets are put under pressure, while being aware of the threat they pose.
"When you are playing against Celtic you have to give it some thought," he added.
"Do you go toe-to-toe with Celtic? I could go toe-to-toe with Celtic and lose 4-0 and be angry about it. I could go to Celtic, be pragmatic and lose 1-0 and be just as angry about it.
"So you have to try and find a balance really."