San Diego manager Jayce Tingler said Arrieta was put on the team's taxi squad after joining the team in Denver for the start of a three-game series.
"We need quality innings, we need pitches, we need an opportunity to win games,'' Tingler said before Monday's 6-5 loss to the Colorado Rockies in which Arrieta did not make an appearance. "With all of his experience, everything he's done, we need some quality innings these last seven weeks and we think he can be part of that solution.
"A great opportunity to pitch, to pitch well, and pitch for a winning team. We'll see how the next couple of weeks line up but it's a great opportunity for both sides.''
Arrieta was released by the Chicago Cubs last week after he was 5-11 with a 6.88 ERA this season in his second stint with the franchise.
The Padres placed Yu Darvish on the 10-day injured list Sunday with lower back tightness. San Diego also is without starting pitcher Chris Paddack, who was placed on the injured list July 31 with an oblique strain.
San Diego (67-54) finished Monday's action with a 1½-game lead over the Cincinnati Reds for the second wild-card spot in the National League.
Arrieta was the NL Cy Young Award winner with Chicago in 2015 and helped the Cubs win the 2016 World Series, their first championship since 1908. He went 68-31 with a 2.73 ERA in 128 starts over five years and threw two no-hitters during his first stint with the team.
He then signed a three-year, $75 million contract with Philadelphia in free agency and went 22-23 with a 4.36 ERA in 64 starts with the Phillies. He had a 4-4 record and a 5.08 ERA in nine starts during the pandemic-shortened 2020 season.
The Associated Press contributed to this report.