McDonald was a hit at Gillingham two seasons ago, notching 25 goals when on loan from Norwich, and after moving on to Coventry he returned to the Kent side this week.
And with five minutes to go he rescued a point for the Gills and made sure they avoided a third straight home defeat - although it was not enough to leapfrog leaders Port Vale, who stay top by a point.
McDonald and co do have a game in hand however - on Tuesday at home to Northampton - and Allen is convinced that his new centre-forward's firepower can see his side end a run of five home matches without a win.
"Everyone wanted three points and to go top of the league," said Allen.
"We started well, it wasn't easy and we made a couple of errors. We're finding it difficult here at the moment to get the results.
"We were top of the league for four and a half months, and the expectation has maybe got on top of the lads a little bit. It makes every other club sit up and make the extra effort
"We'll talk about it but sometimes talk is cheap and we need to get on there and show what we can do. I don't think it'll be too long before we get the victories under our belt here and stride forward again.
"The supporters will be happy Cody has come back, but we want three points, we need the victories at home.
"If we win on Tuesday we can go top again, which will be a huge boost for the players."