The 37-year old Argentine-born former USA international is in his first season as Colorado Rapids head coach and has the team nicely placed in fourth position on the Western Conference table after seven matches.
Donovan played alongside Mastroeni for about a decade with the USA national team as well as for half of the 2013 MLS season when the veteran joined the Galaxy on a short-term deal which has him well-versed to comment on the capabilities of the Rapids boss.
"I don't see any reason why Pablo couldn't lead a team to an MLS Cup," Donovan said ahead of LA's trip to Colorado this weekend.
"If he really wants this and he's passionate about it, he can be as good as he wants to be.
"He's as bright a guy as I've ever played with, and he's very passionate, and I think he will certainly always have the respect of his players, and he'll get the most out of his players.
"Just because you're a great player doesn't always mean that you're going to be a great coach or that you understand the game the right way, but Pablo does very much so, and I think he has a clear sense of the way he wants to play the the way the game should be played."
Mastroeni has so far overseen a record of three wins, two draws and two losses to record 11 points from seven outings but Donovan suggests there is plenty of improvement to come.
"I think they have done a very good job under Pablo," Donovan added. "They've gone on the road and gotten some very good results against good teams, and I think they've been pretty good at home.
"I think when he has time to help shape and mould the team the way he wants, they're going to get even better."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball