The 28-year-old, who can also play as an attacking midfielder, played the last 10 minutes against Norwich City at the Boleyn Ground and the final 12 minutes against Sunderland at the Stadium of Light.
Zarate is now fully fit and he is eager to get more playing time for West Ham after the international break.
“I feel good again now after getting over the injury I had earlier in the season,” the former Lazio star wrote on West Ham’s official website. “The injury was an important one, touching the tendon, but now it has gone and I feel strong.
“We couldn’t rush it, but I’m ready to play again. I’m strong and fast and available if I’m selected.
“The international break is good for me because I can work on the training pitch more than normal to be perfect – at 100 per cent for the next match.”
Zarate has scored one goal and created five chances in four Premier League appearances for West Ham so far this season.
The former Velez Sarsfield star has a pass accuracy of 84% and a shot accuracy of 67%, and has won six dribbles and four tackles.
West Ham are sixth in the Premier League table at the moment with 14 points from eight matches, just a point behind fourth-place Crystal Palace.