Goosen, the two-time US Open champion, was to compete in the 36-hole shoot-out in Ayrshire but his no-show means Robertson, who was a reserve from last week's regional qualifying round at Bruntsfield having been edged out in a play-off, has now been drafted in.
He will join a three-ball that includes the 2013 Amateur champion Garrick Porteous and Scott Henry, the Scottish European Tour player who has a decent pedigree around the robust Gailes links. "I won the Edward Trophy as an amateur when it was played over 72 holes," recalled Henry of that triumph in 2008.
Scott Jamieson and Marc Warren are also among the entrants who will be scrapping for just three automatic places into the Open at Hoylake. The Gailes contest is one of four qualifiers taking place across the UK. Woburn, Sunningdale and Hillside, where triple major champion Vijay Singh is competing, will also offer three Open spots each.
Robertson, meanwhile, will form part of the Scotland side for next week's European Team Championships in Finland. The Scots last won the European crown in 2009 and were beaten by England in last year's final.
The six-man side this year is headlined by newly crowned Amateur champion Bradley Neil, who was part of that losing side 12 months ago and is upbeat about Scotland's hopes.
"We fancy our chances in Finland and I think we have the strongest team probably since Scotland last won the event in 2009," said Neil, who will compete in the Open Championship upon his return from Finland as a reward for his Amateur victory.
"I was invited to play in the Scottish Open [the same week as the European Team event] but I'm obviously committed to helping my team-mates go one better."
Grant Forrest and Jamie Savage, both winners on the international amateur scene this season, are in a side which also includes James Ross and Jack McDonald.
n Scotland men's team for European Team Championships, Linna GC, Finland, July 8-12
G Forrest (Craigielaw), J McDonald (Kilmarnock Barassie), B Neil (Blairgowrie), G Robertson (Glenbervie), J Ross (Royal Burgess), J Savage (Cawder).
Scotland boys' team for European Team Championships, Oslo GC, Norway, July 8-12
G Burns (Williamwood), E Ferguson (Bearsden), C Fyfe (Cawder), B Kinsley (St Andrews), R MacIntyre (Glencruitten), M Naysmith (Marriott Dalmahoy).