King, an 18-year old midfielder, is close to completing a £150,000 move to Swansea after going through his medical at the Welsh club on Monday.
Popular opinion seems to be that the deal would then allow Hearts to sign Skacel - who has been training with the club - for the third time at the end of January. However, Locke's understanding is that Skacel cannot be the player who replaces the youngster.
Administration-hit Hearts are under a continuing Scottish Professional Football League registration embargo, but can apply to replace players with a comparable replacement on a one-out, one-in basis. A separate Scottish Football Association sanction, which prohibits them signing players aged 21 and over, ends on Saturday.
Locke said: "It has to be an under-21 player and it still has to be ratified by the SFA. There's a player I've got in mind who I'd like to bring in. It would be a loan deal.
"We've still got the embargo so it's not a simple case of one in-one out. We've still got to get the okay. Whether we get that or not I don't know."
Skacel can still be signed if Hearts receive clearance from the league that the deactivating of goalkeeping coach Alan Combe's player registration would allow them to bring in a replacement.
"We're still waiting to hear back from the SPFL regarding that," Locke said. "We're hopeful that we will hear something by the end of the day.
"I've not hidden the fact that Skacel is a player I would love to have. It would be great to be able to freshen the squad. Even bringing in one new face would be great for the dressing room."
Hearts take on St Mirren in the Scottish Premiership on Wednesday night buoyed by the news that Billy Brown has agreed another short-term contract with the club's administrators that will keep him in the assistant manager role up until the end of February.
"I'm delighted," added Locke. "I've never hidden the fact I've wanted him beside me all along. We've got some big games coming up so it's important to have Billy still here. Hopefully the by the time this deal expires we'll have sorted everything out off the field, which is the most important thing."
With Hearts 19 points adrift at the bottom of the league table, the League Cup semi-final with Inverness on Sunday might be considered of greater importance than the clash with St Mirren. Unfortunately the limitations of the Hearts squad denies Locke the choice of resting players.
"We'll just have to put out the same team," he said. "It's all we've got. I'd loved to have the scope to make five or six changes ahead of Sunday.
"Then again, tomorrow's a big game off the back of a win and it'll be the first time I'm able to pick the same team two weeks running this year as long as no injuries are picked up in training.
"It's important we keep the run and our increased confidence going."