Sunderland captain Dean Whitehead has been ruled out for six months with a cruciate knee injury.
The 25-year-old midfielder suffered the problem on the eve of his side's Barclays Premier League defeat at Wigan on August 18 and it was initially thought he would only be out for six weeks.
But Keane told Sunderland's official website after last night's 3-0 Carling Cup defeat at Luton: 'It looks as though Deano will need surgery in a couple of weeks.
'It looks like it's a cruciate so that would rule him out for six or seven months. It's been a bad day.
'It's a bitter blow for Deano and for us. We are missing his leadership qualities and his presence.'
Keane confirmed he will look to draft in a midfielder before the transfer window closes and also revealed he had been given permission to talk to Stoke defender Danny Higginbotham and Southampton striker Kenwyne Jones.
Keane said: 'I've been saying for a while that we need to strengthen and we'll look to speak to them tomorrow.'