Hearts have signed striker Paul McCallum from Premier League club West Ham until the end of the season.
The 20-year-old has enjoyed loan spells in the last year at Aldershot and, most recently, Torquay.
McCallum arrives at Tynecastle under the terms of the club's transfer sanctions on a one-out, one-in basis following the sale of teenager Adam King to Swansea.
But an attempt to sign Rudi Skacel for a third spell at the club has been thwarted by the Scottish Professional Football League, after Hearts cancelled the player registration of goalkeeping coach Alan Combe.
Hearts are currently operating under a transfer embargo after entering administration last summer, which also resulted in the team starting the season on minus 15 points.
A statement from the SPFL board read: "In relation to the application to register Rudi Skacel, the board considered a range of factors, including the fact that 34-year-old midfielder Skacel was being proposed to replace a 39-year-old goalkeeper/goalkeeping coach who has not appeared on any first-team squad list in any Premiership match for Heart of Midlothian this season."
Hearts administrator Bryan Jackson said: "I am grateful to the SPFL for the speed and fairness of this decision which allows Adam King to be swiftly replaced with Paul.
"We are disappointed that the application for Rudi Skacel was rejected but understand the reasons for the SPFL's decision."
McCallum is poised to make his debut for Hearts in Sunday's League Cup semi-final against Inverness Caley at Easter Road.