It's not the first time the Spaniard has exited a Grand Slam in the first round, either, withdrawing from the French Open in 2014 with a foot injury.
Almagro later revealed he wasn't there for the huge first round payout, telling the media he already had a healthy wallet.
"I went to court because I think I can play. I was top 10, I have more than 10 million dollars. I'm not going to play for $50,000. It is not the reason," he said after the game.
"I was trying to play during the week. It was tough. I did an MRI and the result wasn't good. That's it. I couldn't play. I felt the problem again on court and I had to retire.
"I considered it (withdrawing) but I was practising, I didn't feel it during the week. I decided to play today."
In other huge Open news, world number four Simona Halep was outed in the first round at Melbourne for the second year in a row, falling in straight sets (6-3, 6-1) to world number 52 Shelby Rogers.