The 27-year old Australian topped 'Boro's scoring list with 14 goals in 36 appearances in all competitions but there is a chance that he could be on his way out of the Riverside Stadium after arriving in February 2010.
"If another club was to ring up with an offer for Scott then it would have to be considered," Mowbray told the Evening Gazette.
"It's the same situation for most of our players.
"But we haven't received any offers for Scott and we have to work on the assumption that what we have got is what we will have.
"If that situation changes, then we will react accordingly."
But Mowbray said that if McDonald was to remain on Teesside then he certainly would still be one of the club's key players.
"He is a committed player. There's no doubt that he will score a lot of goals for us next year," he added.
"Scott's goals were important to us last season, but the main thing that impressed me was his work rate.
"We asked him to do a job for us and he gave it everything he had got. He did a good job for the team."
Mowbray added: "Scott has gone away for the summer but he is loving his football here and he will be ready for next season.
"He could be playing for the Australian national team next month which will help to keep him sharp. But he's one of those players who doesn't like to take any time off."