Celtic full-back Alistair Johnston will be out of action until October, manager Martin O’Neill has confirmed.

The Canada international, 27, went off at half-time in the second game of the season against Kilmarnock, having missed most of the last campaign with a hamstring injury.

Now a scan has revealed he faces another spell on the sidelines.

“There was definitely something there, and I think the prognosis is really that it will be some time in October for him,” said O’Neill prior to the Champions League play-off second leg away to LASK.

Celtic have bolstered their attacking options over the summer and been linked with a number of midfielders and O’Neill concedes the defensive area is one that needs strengthening.

“If you consider that Kieran [Tierney] is essentially our only left-sided full-back, we’ll have a little look,” he added.

“But I really will not concentrate on anything at all until after the game, regardless of what the result is or whichever competition we happen to be in.

“We’ve got some days before the transfer deadline [3 September], and I hope that we will get some people in.”

O’Neill said there was nothing further to report on links with Ermin Mahmic of Slovan Liberec or Torino’s Gvidas Gineitis.

“I was told some weeks ago that we’d lost 14 players and we’d only replaced them with two at the time,” O’Neill continued.

“But I think the whole thing was balanced out. There were some of those players that we took on loan, that were going to be leaving anyway, weren’t going to be coming back. And it was a matter of trying to get a little bit of quality in.

“I think that we could fill up the squad if you wanted to, with loads of names. But it was a bit of quality that we were looking for because that eventually would be, I think, of paramount importance between now and January.”

Colby Donovan, 19, has been deputising for Johnston, impressing in the 3-0 first leg win over LASK at Celtic Park, while Scotland international Anthony Ralston is another option for O’Neill at right-back.