McDonald was today expected to arrive at the north-east club for a medical and to agree personal terms before the transfer window closes overnight, although there is still a chance West Ham or Wigan may come in with a late offer.

Celtic have already turned down a $6 million bid for the Aussie, but Boro boss - and former Celtic coach - Gordon Strachan this weekend came back with an improved figure that Celtic have reportedly accepted, according to reports in Scotland.

McDonald, currently recovering from hernia surgery, missed yesterday's Scottish Premier League game against Hamilton Academicals as current Celtic manager Tony Mowbray turned to new Danish signing Morten Rasmussen instead.

Mowbray admitted this weekend that he couldn't guarantee McDonald gametime and that he might be on his way out the club.

"I can't assure him he will be on the field for 90 minutes of every game, because I've got respect for the other players and that's why you have a squad." Mowbray told The Scotsman. "There is some interest in Scott, I think that's widely known."

Meanwhile Strachan has been busy recruiting some of his favourite players from Celtic during this transfer window, including Kiwi Chris Killen, Stephen McManus, Barry Robson and Willo Flood.

A bid to buy Gary Caldwell failed when Wigan came in with a bigger offer. Both clubs also said to be interested in signing McDonald, but Strachan looks to have been successful this time.

McDonald has scored 65 times from 126 appearances since joining Celtic from Motherwell in 2007, although he has yet to get off the mark for Australia.