The 30-year-old, who is currently competing at Copa America with Chile, has reportedly been deemed surplus to requirements by Ole Gunnar Solskjaer.
And Zamarano believes the former Barcelona attacker must prioritise playing over everything after he started just nine Premier League games last season.
"What's best for [Sanchez] is to play - wherever he can, be it at Manchester United or any other team," Zamorano told Omnisport.
"The important thing is for him to be constantly competing. I talk from my experience. Sometimes when you're abroad and you're not playing, it is hard to regain the level.
"We've seen it. Alexis hasn't played in Manchester for a long time, but the second he puts on the Chilean shirt, he's different. That's what we like.
"No matter how you are doing at your team, we hope at the moment you put on the Chilean shirt you give your best, and that's what Alexis is doing.
"I'm very happy to see him regaining his level and to see him being a vital part of Chile, being a protagonist in South America again."