The study will investigate the safety of once weekly insulin icodec subcutaenously (s.c.) during and after exercise and prolonged fasting in patients with type 2 diabetes (T2D). Participants will first receive insulin decludec (Tresiba®, a long-acting insulin taken once daily) for atleast one week. Afterwards participants will receive insulin icodec that will be administered once weekly at the study site (for a minimum of 7 weeks and maximum of 14 weeks). Insulin icodec is a novel long-acting insulin analogue for once-weekly administration for the treatment of type 2 diabetes. The study will last for about 16-30 weeks. Participant must not participate if participant have suspected hypersensitivity reactions to the study products or cardiovascular diseases within the last 180 days. Female participant cannot take part if she is pregnant, breast-feeding or planning to become pregnant during the study period.

Inclusion Criteria:

• Informed consent obtained before any study-related activities. Study-related activities are any procedures that are carried out as part of the study, including activities to determine suitability for the study.

• Male or female.

• Age 18-75 years (both inclusive) at the time of signing the informed consent.

• Body mass index between 18.0 and 38.0 kilogram per meter^2 (kg/m^2) (both inclusive).

• Glycated hemoglobin (HbA1c) less than or equal to (<=) 9 percent (75 millimoles per mole [mmol/mol]) at screening.

• Treated with basal insulin with or without any of the following anti-diabetic drugs/regimens with stable doses >= 90 days prior to the day of screening:

  • Metformin,
  • Dipeptidyl peptidase 4 (DPP-4) inhibitors,
  • Sodium-Glucose Transport Protein 2 (SGLT2) inhibitors

• Oral combination products (for the allowed individual oral antidiabetic drugs), Injectable and oral glucagon-like peptide 1 (GLP-1) Receptor Agonists.

• Physically active >= 300 metabolic equivalent of task (MET) minutes/week as determined by an International Physical Activity Questionnaire (IPAQ) at screening.

• Mass-specific oxygen volume (VO2) peak greater than (>) 25 milliliters per kilogram per minute (mL/kg/min) as determined by cardiopulmonary testing (CPX) test at screening.

Exclusion Criteria:

• Known or suspected hypersensitivity to study intervention(s) or related products.
• Female who is pregnant, breast-feeding or intends to become pregnant or is of childbearing potential and not using adequate contraceptive method.
• Presence or history of cardiovascular disease including stable and unstable angina pectoris, myocardial infarction, transient ischaemic attack, stroke, cardiac decompensation, clinically significant arrhythmias or clinically significant conduction disorders within 180 days prior to the day of screening.

According to the Novo Nordisk disclosure commitment on novonordisk-trials.com