Call of Duty 4: Modern Warfare — Arcade Mode is Single-Player Only

No. Call of Duty 4: Modern Warfare (2007) **does not support 2-player co-op in Arcade Mode**.

Arcade Mode Details

• Single-player only.
• Replay campaign missions with scoring, time limits, cheats (unlocked), and modifiers.
• Leaderboards for score/time per level.

Co-op Options in CoD4

• Campaign: No co-op (added in MW2 Remastered / MW3).
• Multiplayer: Up to 18 players online (PC) / 12 (console) — competitive only.
• Split-screen: **Not in CoD4.** Introduced in World at War (Nazi Zombies) and MW2 (Spec Ops).

If You Want Co-op CoD

• Modern Warfare 2 (2009): Spec Ops missions (2-player split-screen/online).
• Black Ops series: Zombies (4-player), Dead Ops Arcade.
• MW (2019) / MWII / MWIII: Spec Ops, Raids, DMZ (3-player).

CoD4 Arcade Mode is a solo score-attack replay tool — nothing more.