In Gita, Krishna has established his identity with all the 3 famous deities: BrahmA -- Vishnu -- Shiva[linga]. This implies that all the ultimate gods are in oneness of supreme One. My answer is based on how Vishnu is depicted in popular culture.
Excerpts from this post;
There is a namesake Vishnu reference, which refers to the sons of Aditi:
BG 10.21 - Among the Adityas [viz Dhata, Mitra, Aryama, Rudra, Varuna, Surya, Bhaga, Vivasvan, Pusa, Savita, Tvasta and Visnu.-Tr.] I am Vishnu; ... -- translation Gambhirananda
Few verses in chapter-11 depicts the famous all deity form:
BG 11.10 - Having many faces and eyes, possessing many wonderful sights, adorned with numerous celestial ornaments, holding many uplifted heavenly weapons;
BG 11.15 - Arjuna said O God, I see in Your body all the gods as also hosts of (various) classes of beings; Brahma the ruler, sitting on a lotus seat, and all the heavenly sages and serpents.
BG 11.16 - I see You as possessed of numerous arms, bellies, mouths and eyes; as having infinite forms all around. O Lord of the Universe, O Cosmic Person, I see not Your limit nor the middle, nor again the beginning!
BG 11.17 - I see You as wearing a diadem, wielding a mace, and holding a disc; a mass of brilliance glowing all around, difficult to look at from all sides, possessed of the radiance of the blazing fire and sun, and immeasurable.
BG 11.22 Those who are the Rudras, the Adityas, the Vasus and the Sadhyas, the Visve (-devas), the two Asvins, the Maruts and the Usmapas, and hosts of Gandharvas, Yaksas, demons and Siddhas-all of those very ones gaze at You, being indeed struck with wonder.
BG 11.23 - O mighty-armed One, seeing Your immense form with many mouths and eyes, having numerous arms, thighs and feet, with many bellies, and fearful with many teeth, the creatures are struck with terror, and so am I.
Another famous depiction of Vishnu is sleeping on Adi Shesha is discussed here.
Another form depicts as of whole universe silently pervades as the Vishnu:
BG 9.4 - This whole universe is pervaded by Me in My unmanifested form. All beings exist in Me, but I am not contained in them!