It's not quarterback, certainly not running back or wide receiver.
Try offensive tackle.
"The tackle situation is a question because we've lost two guys that we didn't anticipate losing," Swinney said. "Giff Timothy, who had a year left and had been a two year starter for us -- we lost Patrick Destefano, who really was on his way to being a starter for us and an outstanding player.
"We lose two guys off an off cycle, that's a huge, huge question, so kind of settling that out."
Isaiah Battle, who started the final four games in 2013 at right tackle, is expected to replace Brandon Thomas at left tackle. Two of the top candidates at right tackle are experienced. Shaq Anthony started three games there a season ago. Joe Gore logged 58 snaps over seven games.
"Shaq's got good experience and he's done some good things for us when they count," Swinney said. "Joe Gore, he's really what you're looking for, he really has all the tools to be an outstanding player. It's just a matter of putting it together and staying healthy, avoiding some of the setbacks that he's had as a young player. This junior year is big for him.
"Maverick Morris, is he going to be a guy that catches our attention? I like what I've seen from him, as far as the offseason, how he's worked in the mat drills and some of the things I saw at bowl practice from him. Now, can he put it together and execute what we're trying to do."
Kalon Davis, a seven game starter at guard in 2013, could also figure into the mix at tackle.
"He's very smart, moves well, I think he's going to have a better than average shot of playing guard and tackle," Swinney said. "That's kind of the jigsaw puzzle, the biggest question to me. We'll move a lot of guys around. We've got some veteran guys. We're going to get them out of their comfort zone a little bit. We've just got to put it all together, find out who the best five are. We've got good flexibility, as far as being able to move those guys around up front."
David Beasley split starts with Davis at left guard last season. Ryan Norton started in every game at center.
"I like the guys that we have. We've just got to develop," Swinney said. "We've got Isaiah Battle and Eric MacLain is going to play both. He's going to go into spring starting off at guard, as our start, we're going to give him a chance to be a starter. Feel like he's earned that opportunity. We'll see what he does with that and he's also going to have to put his hand in at tackle."
This much is known: Beasley and Anthony will be suspended for the season opener against Georgia because of a violation of team rules.
"Mac is a guy that we really felt like deserved a chance to be the guy. He is really, talk about a fully committed guy that has worked really, really hard," Swinney said. "David Beasley is a guy that, obviously, can win for us. We think the world of David as a player. He's got a ton of talent and has won a bunch of games for us, but we've got to refocus him a little bit. He's going to have to earn that. If he's the best player, he'll earn it.
"Regardless of suspension, [Beasley] wouldn't have been the first player, going into spring ball, I can tell you that."
Dabo's biggest concern on offense
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