Mark Middlemas, managing partner at Universal McCann, said that a tie-up between the two companies would "decimate" recent progress by GCap in building up its commercial links following the GWR and Capital merger.
He said: "You can't describe culture on a balance sheet, and while I'm all for consolidation, the culture thing is massively important, as we found with the GWR and Capital merger."
Middlemas also noted that the GWR and Capital merger had a knock-on effect on radio buyers, while GCap smoothed out its structure and strategy: "We had pain for about 18 months - the change certainly affected their service," he said.
Meanwhile, it has emerged that GCap's major investors are refusing to meet Global until after they hear chief executive Fri Hazlitt detail her new strategy for the company on 11 February. According to recent press reports, Global is now looking to acquire Virgin Radio.
A source close to GCap said: "This bodes very well for GCap because it shows the shareholders are giving Fru a chance. The view in the industry seems to be that Global is looking a bit desperate."