The USA international cast doubt over his future at the end of 2012 when he indicated that he may bring his playing days to a close after reassessing things in the MLS offseason.
Arena, who led the Galaxy to back-to-back MLS Cups last season, says that ex-Everton loanee Donovan will be back at The Home Depot Center this campaign but was unsure exactly when the 30-year old will return to training.
"We've given him a little more time off," Arena said.
"He's definitely playing this year, but we're just working out a return date that makes sense for all of us we're working that out soon."
Arena added of Donovan's potential retirement: "No, I thought he was going to come back. I think he just needs a little bit more of an extended leave of absence. He's got a couple of years that have taken its toll and he needs a little bit more time.
"He like any player needs the right time. The longer that he takes off, it'll take him longer to be ready to play. Generally, we'd like to see some players get three or four weeks to bring their fitness along."