Slaughter and May is at risk of losing up to six high-profile clients after the firm's decision to handle back-to-back sell-side mandates during the past 12 months.
Slaughters has conceded that it expects to lose logistics giant Exel as a client following the company's takeover by Linklaters client Deutsche Post.
Slaughters corporate partner Nigel Boardman said: "You have to accept that takeovers will lead to client attrition over time. You therefore have to be confident about winning new clients."
Meanwhile, the firm will have to battle it out against Allen & Overy (A&O) for a place on Alliance Boots' first-ever legal panel.
Slaughters acted for both legacy companies, but advised Boots on the £7bn merger with Alliance UniChem, which was advised by A&O. Despite the newly merged entity installing both firms as joint advisers, general counsel Marco Pagni warned that both will have to participate in next month's tender exercise.
Slaughters will also be watching events at client BOC Group closely, which will also review its external legal advisers after the company agreed to be taken over by German-based Linde.
In addition to Exel, Alliance Boots and BOC, Slaughters has advised the targets on the takeovers of Pilkington and House of Fraser by Nippon Sheet Steel and Bauger respectively.