The 25-year-old forward moved to Upton Park from Sochaux in July 2012 but started just two Premier League games in his debut campaign, scoring twice.
However, after the Mali international bagged a double in Saturday's 3-0 pre-season win over Eintracht Braunschweig, McDonald expects him to have a greater impact next term.
|7/4||West Ham are 7/4 with Bet365 to finish in the top half of the Premier League
"He was running in behind and causing problems, which is great to see as it stretches teams. It was a huge improvement on the last few games we've played.
"Modibo's ability is there as we paid a fair bit of money for him. When you sign new players sometimes they take a bit longer to settle into the team. He's got one hell of a chance to start the season."
Maiga is also likely to face stiffer competition for a starting berth next term, with Sam Allardyce looking to further bolster his strikeforce following the £15 million acquisition of Andy Carroll.
"I know there are a lot of names being bandied about but I do feel that we need another striker to provide competition for places," McDonald added.
"I think we've got good competition for every other place in the team at the moment and, over the three games in Germany, everyone played their part and impressed when they got their opportunity."