He urged members to look beyond personal interests and prioritise the party.
"If everyone is behind Ahmad Zahid, there is no issue.
"But if everyone has different views and continue with their differences, that will lead the party to split," he told reporters at the Parliament lobby on Wednesday (July 3).
Ismail said this after being asked to comment on Datuk Seri Hishammuddin Hussein's remark that Ahmad Zahid's return should not lead to internal bickering.
"We are in a good position now compared to last year.
"I'm not holding a high party post and am merely a division chief and a member who loves the party," added the Sembrong MP.
On Sunday, Ahmad Zahid said he was now back as Umno president after having taken leave from the post in December.
Ismail said there were bigger issues to address than questioning who helmed the party.
He said the issue should not arise as Ahmad Zahid's position as president was determined at the party election last year.
Asked to comment on the five leaders who were appointed the party's supreme council members, Ismail said it was the prerogative of the party president.
Batu Pahat division chief Datuk Mohd Puad Zarkashi, Hulu Langat division chief Datuk Johan Abd Aziz, Bagan division chief Datuk Shaik Hussein Mydin, Sepanggar division chief Datuk Yaakub Khan and Seputeh division vice-chief Datuk Razlan Muhammad Rafii have been roped into the supreme council.