But since Rios was acquired by the White Sox on waivers this month, Snider has switched to the other side of the field. He has played in right in the nine games he's spent with the Jays since being recalled.
"What's unfair to him is that he was playing left field the whole time he was in Triple-A, and once Rios got picked up on waivers, then they put him in right field," Gaston said. "So he's been used to playing left field, and to change is hard."
Snider may have spent more time in left field recently, but has plenty of experience in right.
"I've played right field my whole amateur career, other than when I pitched and caught, when I was younger, so it's kind of a natural position for me that hopefully comes back," Snider said. "Last year I started the year in right field too, and played half the season there, so the adjustment to left field was a little different.
"Since I've played primarily in left this year, a little bit of an adjustment going back, but it's more just the angles of the throws and things that as you get more reps, work in BP, it comes back pretty quick."
The rookie felt his play in right field has been OK so far, and he has been working on making the necessary adjustments to his new position.
"Hitting the cutoff man probably is the No. 1 thing right now I'm working on, and just making sure I'm getting myself in a good position to make throws down the line," said Snider, who throws left-handed. "In left field, you just spin and come up firing. In right field, you've got to backhand it or come around it.
"There's a little bit of footwork change, but it's something that I've done before and feel confident that I can get back to where I was before."
For Gaston, Snider's future ultimately lies in left field, which is currently occupied by Adam Lind. Lind, who's having a breakout year, split time in left field and as a designated hitter when Snider was with the club at the beginning of the season.
Snider has "an average arm out there and sometimes in right field you need a little bit above-average arm," Gaston said. "He's been used to playing left field, and to change is hard. He might find it easier -- left field is tougher to play -- but unfairly to him, he had to go to right field.
"I think I'd like to see him in left field if we could. If it doesn't work out that way, then he can play right. ... I'll try not to move him unless I have to."