Roberts came off the bench to net the winning goal for the second consecutive game in Rovers' 2-1 victory at Newcastle, although he appeared reluctant to receive congratulations from the rest of the team as he pointed to the name on the back of his shirt.
The 32-year-old also scored his side's second goal in their 2-1 win over Wigan on Saturday having been introduced as a substitute, but a 45-minute cameo in the match before that against Chelsea was Roberts' only other appearance this season and his reaction could be viewed as a message to manager Sam Allardyce.
McDonald said he had not spoken to Roberts about the celebration, but suggested the player should just continue hitting the back of the net to make a case for first-team selection.
"It's slightly disappointing when you score a goal and you don't celebrate with your team-mates, but he's pleased to be scoring goals and he's trying to prove a point," McDonald said.
"Keeping on scoring goals is the perfect way to do that.
"He has come on and over the last three games he has had three really good chances.
"He's taken two of them and that's the response the manager wants - if you are not in the team, you have to come and show him that you need to be in there.
"He's done that and the manager probably has another problem now."
There was controversy in the game at St James' Park following an incident where Joey Barton struck Rovers midfielder Morten Gamst Pedersen.
As referee Michael Jones did not punish Barton, the Newcastle player has been charged with violent conduct by the Football Association after he lashed out with a blow that caused Pedersen to fall to the ground.
Like Allardyce, McDonald is content to let the FA deal with the matter, although he did condemn what he felt was an unprovoked attack.
"It's obviously foolish and it's the wrong thing to do, but no doubt the powers that be will sort that out," McDonald said.
"The pictures are there, it wasn't provoked and I'm sure they will make the right decision about what to do."
When it was put to him that the contact Barton made with Pedersen was a "full-blooded punch", McDonald said: "Yes it was, and it was unprovoked as well, which probably makes it worse."
Another major talking point from the action was the team Ian Holloway fielded for Blackpool's 3-2 defeat at Aston Villa.
The Premier League have confirmed they are investigating Holloway's decision to make 10 changes - and put out what could be perceived as a weakened side - for the match, but McDonald believes what the Seasiders boss did was within his rights.
"A lot of the squad work very hard to try and get into the team and when they are given the chance they have to try and take it," McDonald said.
"Blackpool almost did that last night and it is totally for Ian Holloway to pick whatever team he wants.
"He works with the players day in, day out, he knows what they can and can't do and he almost got the result in the end.
"The squad of 25 means that if a player is in it, and is fit and available, he is good enough to pay in the first team. That is what happened last night."