But there could be more twists to the tale because they have also agreed deals for Aberdeen striker Lee Miller and Coventry’s Leon Best ... as back-up!
McDonald has remained Boro’s main target once Celtic indicated they would consider dropping their asking price of £3.5m.
It appears that Boro were hoping to complete a deal for around £2m and it looked as though protracted negotiations were nearing completion by early afternoon.
The Australian striker, who has been with Celtic since 2007 after Strachan signed him from Motherwell, has scored 65 times in 126 appearances for the Hoops.
It is believed McDonald wants to test himself in England again, having had unsuccessful spells with Southampton and Wimbledon in his earlier career.
Boro were reported to have potential opposition from West Ham this afternoon, and it’s obvious that the Hammers have the cash following the recent takeover.
Celtic boss Tony Mowbray: “If Scott’s still here on Tuesday, when we play Kilmarnock, I’ll be delighted. I want Scott to stay with us because he’s Celtic’s top scorer and makes an enormous contribution to the club.
“There’s never been any evidence of a disagreement between us. Scott’s a sensible, likeable boy and we’ve never had a cross word.
“There's either harmony or disharmony between a player and a manager and I’d say the two of us get on fine. I’m certainly not pushing Scott out of the club because I appreciate him too much.”