Andrea Ranocchia insists Inter's players are seeking revenge after Frank de Boer was sacked as head coach following a string of poor results.
The Dutchman took charge at the start of the season following Roberto Mancini's sacking, but lost his job after 85 days on Wednesday with his side sitting 12th in Serie A having lost four of their last five league games.
Youth coach Stefano Vecchi will step in to manage Inter's trip to Southampton in the Europa League, and Ranocchia stressed the squad must now stand up and be counted.
"We are professionals - we have seen a lot," he told a pre-match news conference. "We are sorry for De Boer and there is a desire for revenge on our part.
"This is a difficult time, but it is a great opportunity to show that we are still alive and kicking. There are no more excuses. Now, we must react."
Vecchi added that he had a good relationship with De Boer, but is looking forward to the opportunity to lead Inter.
"I was contacted by [director of sport] Piero Ausilio to train the first team," he said. "My staff and I know the guys, because we train together.
"I'm sorry for De Boer. Our relationship was good, unfortunately these things happen in football.
"I am thankful to [owners] Suning, and I also thank president Erick Thohir and Ausilio for this opportunity.
"We must live in the present and focus on the Southampton game. We need to prepare at our best."
Inter travel to St Mary's on Thursday boosted by a 1-0 win over the Saints at San Siro last month, with Antonio Candreva on the score-sheet.
However, those have been the only three points collected by the Milan outfit in this European campaign, and they sit bottom of Group K.