In plain words
The great warriors will think you withdrew from battle out of fear; those who held you in high regard will come to think little of you.
Word for word
The great chariot-warriors will think you withdrawn from battle out of fear; and having been highly esteemed by them, you will go to lightness.
The commentators
Bhagavadgītābhāṣyam
किञ्च —
भयात् कर्णादिभ्यः रणात् युद्धात् उपरतं निवृत्तं मंस्यन्ते चिन्तयिष्यन्ति न कृपयेति त्वां महारथाः दुर्योधनप्रभृतयः । येषां च त्वं दुर्योधनादीनां बहुमतो बहुभिः गुणैः युक्तः इत्येवं मतः बहुमतः भूत्वा पुनः यास्यसि लाघवं लघुभावम् ॥ ३५ ॥
In plain words
And there is more —
'Out of fear' — fear of Karṇa and the rest. 'From the battle' — from the fighting. 'Withdrawn' — turned back. That is what they will think, what will run in their minds about you: that you left out of fear, and not out of any compassion — those great chariot-warriors, Duryodhana and the others. And these very men, Duryodhana and his side, in whose eyes you stood 'highly regarded' — held to be a man furnished with many excellences, that is how they rated you — after standing that high, you will come to 'lightness': to counting for nothing.
Close to the Sanskrit
And what further —
'Out of fear' — from Karṇa and the rest; 'from the battle' — from the fighting; 'withdrawn' — turned back: so will they think, will they consider, of you — not out of compassion — the great chariot-warriors, Duryodhana and the rest. And those in whose eyes — Duryodhana's and the others' — you were 'highly regarded', that is, endowed with many virtues and so regarded: having been highly regarded, you will thereafter go to 'lightness', to the state of being slight.