The ubiquitous interactions between tumor cells and the surrounding microenvironment contribute to tumor metastasis, interrupting these communications has, therefore, a great potential for antimetastasis therapy. Here, we describe an in situ self-assembly strategy that limits direct contact between tumor cells and the tumor microenvironment (TME). In this strategy, the Lys-Leu-Val-Phe-Phe (KLVFF) peptide motifs are targeted to the tumor by hyaluronic acid (HA) functionalized liposomes and spontaneously undergo self-assembly to form nanofibers with a net-like structure wrapping around tumor cells. The fibrous nanostructures bury the membrane protrusions and thus hinder the migration and invasion of tumor cells, especially the transmigration through the fenestrated endothelium. The nanofibril coatings on tumor cells significantly block tumor cells induced platelet aggregation in vitro and prevent the adhesion of platelet around circulating tumor cells (CTCs) in vivo, thus limit the pro-metastasis effect of platelets and prevent the early metastasis. Furthermore, the nano-nets stably retain in the primary tumor site for over 72 h and effectively prevent the activation of intratumoral platelet, which suppress tumor progression and the spontaneous lung metastasis in 4T1 breast cancer mice model. Our study paves a promising avenue to combat tumor metastasis by regulating the interactions between tumor cells and the TME.Copyright © 2020 Elsevier Ltd. All rights reserved.