Martin O'Neill admits he does not know if he would "have the energy" to stay on as Celtic boss past the end of the season.
The 73-year-old has returned to the Glasgow club following the departure of Wilfried Nancy, 33 days after making way for the Frenchman following an interim spell in which he won seven out of eight matches.
Former Republic of Ireland boss O'Neill has been installed until the end of the campaign, but is not certain he would be able to push himself on again past the summer.
"I can't see that for a start and I genuinely can't. I don't know whether I would have the energy and all that type of stuff," O'Neill said on talkSPORT when asked if he would feel like staying on should the campaign finish on a positive.
"I will just put everything into it now for these next couple of months and the same applies to me - if I don't win football matches I'll be straight under pressure and that starts here at the weekend."
Having come in to steady the ship after the exit of Brendan Rodgers, O'Neill left Celtic level on points with Scottish Premiership leaders Hearts with a game in hand and nine points ahead of Rangers.
However, Celtic lost six out of eight matches under Nancy and are now six points behind Hearts with the same number of matches played - and would be three off Rangers in third if the Light Blues beat Aberdeen at Ibrox on Tuesday.
"It will be very, very difficult. We are behind," O'Neill said on Celtic's title hopes.
"Rangers have caught up now as well too and so it will be difficult, but it's a challenge for us."
Meanwhile, Celtic have ended the loan spell of Manchester City youngster Jahmai Simpson-Pusey, who will now spend the rest of the season with Cologne.
PA
