diff --git a/.changelog/10872.txt b/.changelog/10872.txt
new file mode 100644
index 000000000000..cad56420499f
--- /dev/null
+++ b/.changelog/10872.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+consul/connect: Avoid assumption of parent service when syncing connect proxies
+```
diff --git a/command/agent/consul/group_test.go b/command/agent/consul/group_test.go
index 550bd72b3d55..a76aac73e1f8 100644
--- a/command/agent/consul/group_test.go
+++ b/command/agent/consul/group_test.go
@@ -77,11 +77,6 @@ func TestConsul_Connect(t *testing.T) {
 		},
 	}
 
-	// required by isNomadSidecar assertion below
-	serviceRegMap := map[string]*consulapi.AgentServiceRegistration{
-		MakeAllocServiceID(alloc.ID, "group-"+alloc.TaskGroup, tg.Services[0]): nil,
-	}
-
 	require.NoError(t, serviceClient.RegisterWorkload(BuildAllocServices(mock.Node(), alloc, NoopRestarter())))
 
 	require.Eventually(t, func() bool {
@@ -102,7 +97,7 @@ func TestConsul_Connect(t *testing.T) {
 
 		require.Contains(t, services, serviceID)
 		require.True(t, isNomadService(serviceID))
-		require.False(t, isNomadSidecar(serviceID, serviceRegMap))
+		require.False(t, maybeConnectSidecar(serviceID))
 		agentService := services[serviceID]
 		require.Equal(t, agentService.Service, "testconnect")
 		require.Equal(t, agentService.Address, "10.0.0.1")
@@ -112,7 +107,7 @@ func TestConsul_Connect(t *testing.T) {
 
 		require.Contains(t, services, connectID)
 		require.True(t, isNomadService(connectID))
-		require.True(t, isNomadSidecar(connectID, serviceRegMap))
+		require.True(t, maybeConnectSidecar(connectID))
 		connectService := services[connectID]
 		require.Equal(t, connectService.Service, "testconnect-sidecar-proxy")
 		require.Equal(t, connectService.Address, "10.0.0.1")
diff --git a/command/agent/consul/service_client.go b/command/agent/consul/service_client.go
index da44319660b8..3a22848f0984 100644
--- a/command/agent/consul/service_client.go
+++ b/command/agent/consul/service_client.go
@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/url"
 	"reflect"
+	"regexp"
 	"strconv"
 	"strings"
 	"sync"
@@ -816,7 +817,7 @@ func (c *ServiceClient) sync(reason syncReason) error {
 		}
 
 		// Ignore if this is a service for a Nomad managed sidecar proxy.
-		if isNomadSidecar(id, c.services) {
+		if maybeConnectSidecar(id) {
 			continue
 		}
 
@@ -886,7 +887,7 @@ func (c *ServiceClient) sync(reason syncReason) error {
 		}
 
 		// Ignore if this is a check for a Nomad managed sidecar proxy.
-		if isNomadSidecar(check.ServiceID, c.services) {
+		if maybeSidecarProxyCheck(id) {
 			continue
 		}
 
@@ -1681,8 +1682,14 @@ const (
 	sidecarSuffix = "-sidecar-proxy"
 )
 
-// isNomadSidecar returns true if the ID matches a sidecar proxy for a Nomad
-// managed service.
+// maybeConnectSidecar returns true if the ID is likely of a Connect sidecar proxy.
+// This function should only be used to determine if Nomad should skip managing
+// service id; it could produce false negatives for non-Nomad managed services
+// (i.e. someone set the ID manually), but Nomad does not manage those anyway.
+//
+// It is important not to reference the parent service, which may or may not still
+// be tracked by Nomad internally.
+//
 //
 // For example if you have a Connect enabled service with the ID:
 //
@@ -1692,14 +1699,39 @@ const (
 //
 //	_nomad-task-5229c7f8-376b-3ccc-edd9-981e238f7033-cache-redis-cache-db-sidecar-proxy
 //
-func isNomadSidecar(id string, services map[string]*api.AgentServiceRegistration) bool {
-	if !strings.HasSuffix(id, sidecarSuffix) {
-		return false
-	}
+func maybeConnectSidecar(id string) bool {
+	return strings.HasSuffix(id, sidecarSuffix)
+}
 
-	// Make sure the Nomad managed service for this proxy still exists.
-	_, ok := services[id[:len(id)-len(sidecarSuffix)]]
-	return ok
+var (
+	sidecarProxyCheckRe = regexp.MustCompile(`^service:_nomad-.+-sidecar-proxy(:[\d]+)?$`)
+)
+
+// maybeSidecarProxyCheck returns true if the ID likely matches a Nomad generated
+// check ID used in the context of a Nomad managed Connect sidecar proxy. This function
+// should only be used to determine if Nomad should skip managing a check; it can
+// produce false negatives for non-Nomad managed Connect sidecar proxy checks (i.e.
+// someone set the ID manually), but Nomad does not manage those anyway.
+//
+// For example if you have a Connect enabled service with the ID:
+//
+//	_nomad-task-5229c7f8-376b-3ccc-edd9-981e238f7033-cache-redis-cache-db
+//
+// Nomad will create a Connect sidecar proxy of ID:
+//
+// _nomad-task-5229c7f8-376b-3ccc-edd9-981e238f7033-cache-redis-cache-db-sidecar-proxy
+//
+// With default checks like:
+//
+// service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:1
+// service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:2
+//
+// Unless sidecar_service.disable_default_tcp_check is set, in which case the
+// default check is:
+//
+// service:_nomad-task-322616db-2680-35d8-0d10-b50a0a0aa4cd-group-api-count-api-9001-sidecar-proxy
+func maybeSidecarProxyCheck(id string) bool {
+	return sidecarProxyCheckRe.MatchString(id)
 }
 
 // getNomadSidecar returns the service registration of the sidecar for the managed
diff --git a/command/agent/consul/service_client_test.go b/command/agent/consul/service_client_test.go
index 5a72c4a0e6ce..9cacaa38ddce 100644
--- a/command/agent/consul/service_client_test.go
+++ b/command/agent/consul/service_client_test.go
@@ -624,3 +624,19 @@ func TestSyncOps_empty(t *testing.T) {
 	try(&operations{}, true)
 	try(nil, true)
 }
+
+func TestSyncLogic_maybeSidecarProxyCheck(t *testing.T) {
+	try := func(input string, exp bool) {
+		result := maybeSidecarProxyCheck(input)
+		require.Equal(t, exp, result)
+	}
+
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy", true)
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:1", true)
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:2", true)
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001", false)
+	try("_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:1", false)
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy:X", false)
+	try("service:_nomad-task-2f5fb517-57d4-44ee-7780-dc1cb6e103cd-group-api-count-api-9001-sidecar-proxy: ", false)
+	try("service", false)
+}