The Australian international paid for the chances he missed in the goalless draw against Hamburg in the Europa League on Thursday night when he was left on the bench for yesterday's trip to Falkirk in the Clydesdale Bank Premier League.
Howe
ver, when the Hoops went behind to a Pedro Moutinho volley in the second half, after Scott Arfield's penalty had cancelled out Gary Caldwell's opener, McDonald was thrown on in place of Paddy McCourt to try to rescue the game.
The former Motherwell striker had barely been on the pitch for five minutes when he headed in the equaliser and minutes later he side-footed in from close range to give the visitors the lead.
The Bairns earned a point, though, in the 83rd minute through substitute Mark Stewart to scupper Celtic's hopes of going four points clear of Old Firm rivals Rangers at the top of the table.
Mowbray threw down the gauntlet to McDonald, saying: "There is competition for places but I'm delighted that he scored a couple of goals.
"From my perspective, you'd like to be in the position where you don't leave Scott on the bench because he scores every single week.
"But he has had a few weeks where he has had some chances and the keeper has made good saves but hopefully those goals will help his confidence."
Mowbray claimed his side were "mentally tired" from their trip to Germany in midweek.
"It was a tired performance from us," he said.
"It was probably as poor as we've been this season and the team didn't play well in the first half.
"It was the same defence which kept a clean sheet in Hamburg but mentally it was a tough day for the team. Generally, we have had mentally-tired performances after games in Europe and I think that was one.
"Yet, if we want to take a positive, the team tried to rally themselves from a losing position and showed great endeavour to get back into a winning position.
"They could have felt sorry for themselves, they had a tough week, getting back from Europe in the early hours (of Friday).
"Obviously, we are disappointed to drop points but we have to move on."
Despite their best performance of the season, Falkirk remain at the bottom of the SPL with five points.
Manager Eddie May, who also saw keeper Robert Olejnik make a remarkable penalty save from Aiden McGeady just before the break – saving from the rebound after blocking the Celtic midfielder's first attempt – will take heart from the performance.
He said: "We have to ask every player to play to their maximum and, if we can do that, we have a chance of staying in the league."
